We are constantly confronted with different chemical interactions. The combustion of natural gas, iron rusting, whisk of milk - not all processes that are studied in detail in the school course of chemistry.

For the flow of some reactions, the fractions of seconds are required, and for some interactions, days and weeks are needed.

Let's try to identify the dependence of the reaction rate on temperature, concentration, other factors. In a new educational standard, a minimum number of academic times is given to this question. In the tests of the Unified State Exam, there are tasks for the dependence of the reaction rate on temperature, concentration and even the calculated tasks are proposed. Many high school students experience certain difficulties with the search for answers to these questions, therefore, we analyze this topic in detail.

The relevance of the question under consideration

Information on the reaction rate has important practical and scientific importance. For example, in the specific production of substances and products from this value directly depends on the performance of the equipment, the cost of goods.

Classification of leaking reactions

There is a direct relationship between the aggregate state of the initial components and products formed during heterogeneous interactions.

Under the system it is customary to imply in the chemistry of the substance or their aggregate.

Homogeneous consider such a system that consists of one phase (the same aggregate state). As its example, you can mention a mixture of gases, several different liquids.

Heterogeneous is a system in which reacting substances are in the form of gases and liquids, solids and gases.

There is not only the dependence of the reaction rate of the temperature, but also on which phase the components entering the analyzed interaction are used.

For homogeneous composition, the process is characterized by the process throughout the volume, which significantly increases its quality.

If the starting materials are in different phase states, in which case the maximum interaction is observed on the border of the phase partition. For example, when the active metal is dissolved in acid, the formation of the product (salt) is observed only on the surface of their contact.

Mathematical relationship between process speed and various factors

What does the chemical response speed equation look like from temperature? For a homogeneous process, the rate is determined by the amount of substance that enters into the interaction is either formed during the reaction in the amount of the system per unit of time.

For the heterogeneous process, the rate is determined by the amount of substance reacting or obtained in the process on a unit area in a minimum period of time.

Factors affecting the rate of chemical reaction

The nature of the reactant substances is one of the reasons for different flow rate of processes. For example, alkali metals at room temperature are formed with alkali water, and the process is accompanied by intense release of hydrogen gaseous hydrogen. Noble metals (gold, platinum, silver) are not capable of similar processes at room temperature, nor when heated.

The nature of the reactant substances is the factor that is taken into account in the chemical industry to increase the profitability of production.

The relationship between the concentration of reagents and the speed of leakage of the chemical reaction was revealed. What it will be higher, the more particles will face, therefore, the process will flow faster.

The law of the active masses in mathematical form describes a direct proportional relationship between the concentration of the starting materials and the speed of flowing.

It was formulated in the middle of the nineteenth century by the Russian chemist N. N. Beketov. For each process, the reaction constant is determined, which is not associated with either the temperature or with a concentration, nor with the nature of the reacting substances.

In order to speed up the reaction in which the solid is involved, it is necessary to chop it to a powder condition.

At the same time, an increase in surface area occurs, which positively affects the speed of the process. For diesel fuel, a special injection system is used, due to which it is in contact with air, the speed of the combustion process of the mixture of hydrocarbons increases significantly.

The heating

The dependence of the speed of the chemical reaction on temperature is explained by the molecular-kinetic theory. It allows you to calculate the amount of collisions between reagent molecules under certain conditions. If you are armed with such information, then under normal conditions, all processes must occur instantly.

But if we consider a specific example of the dependence of the reaction rate from temperature, it turns out that for interaction it is necessary to first break the chemical bonds between atoms so that new substances are formed. This requires significant energy costs. What is the dependence of the reaction rate of temperature? The activation energy determines the possibility of rupture molecules, it is it that characterizes the reality of the processes. Its units of measurement is KJ / mol.

With an insufficient energy indicator, the collision will be ineffective, so it is not accompanied by the formation of a new molecule.

Graphic representation

The dependence of the speed of the chemical reaction on temperature can be represented graphically. When heated, the number of collisions between particles increases, which contributes to the acceleration of interaction.

What does the response rate of the reaction rate differ? The horizontal is deposited by the energy of molecules, and the vertical is indicated by the number of particles having a high energy supply. The schedule is a curve for which one can judge the speed of the specific interaction.

The greater the difference between the average of the average, the further is from the maximum point of the curve, and the smaller percentage of molecules has such a stock of energy.

Important aspects

Is it possible to record the equation of the dependence of the reaction rate constant on temperature? Its increase reflects on increasing the speed of the process. This dependence is characterized by a certain value of the temperature coefficient of the process rate.

For any interaction, the dependence of the response rate constant was revealed. In the case of its increase by 10 degrees, an increase in the speed of the process is 2-4 times.

The dependence of the rate of homogeneous reactions on temperature can be represented in mathematical form.

For most interactions at room temperature, the coefficient is in the range from 2 to 4. For example, when the temperature coefficient is 2.9, the temperature increase by 100 degrees speeds up the process almost 50000 times.

The dependence of the reaction rate on temperature can easily be explained by different types of activation energy. It has a minimum value when conducting ion processes, which are determined only by the interaction of cations and anions. Numerous experiments indicate the instantaneous course of such reactions.

With a high value of activation energy, only a small number of collisions between particles will lead to interaction. With an average activation energy value, the reagents will interact at an average rate.

Tasks for the dependence of the reaction rate from concentration and temperature are considered only on the eldest stage of learning, they often cause serious difficulties from the guys.

Measuring the speed of proceeding process

Those processes that need substantial activation energy suggest the initial gap or weakening bonds between atoms in the source substances. At the same time, their transition occurs in a certain intermediate state, called the activated complex. It is an unstable state, quite quickly disintegrates the reaction products, the process is accompanied by extraction of additional energy.

In the simplest embodiment, the activated complex is a configuration of atoms with weakened old connections.

Inhibitors and catalysts

Analyze the dependence of the speed of the enzymatic reaction from the temperature of the medium. Such substances carry out the process of process accelerators.

They themselves are not participants in the interaction, their number after the completion of the process remains unchanged. If catalysts contribute to an increase in the reaction rate, then inhibitors, on the contrary, slow down this process.

This is the formation of intermediate compounds, resulting in a change in the speed of the process.

Conclusion

In the world every minute a variety of chemical interactions occur. How to establish the dependence of the reaction rate of temperature? The Arrhenius equation is a mathematical explanation of the communication of the velocity constant and temperature. It gives an idea of \u200b\u200bthose values \u200b\u200bof activation energy, under which the destruction of either weakening bonds between atoms in molecules is possible, the distribution of particles into new chemicals.

Thanks to the molecular-kinetic theory, it is possible to predict the likelihood of interactions between the initial components, to calculate the rate of proceedings. Among those factors that have an impact on the reaction rate, it is of particular importance to change the temperature indicator, the percentage concentration of interactive substances, the surface area of \u200b\u200bthe contact, the presence of the catalyst (inhibitor), as well as the nature of the interacting components.

Some chemical reactions occur almost instant (the explosion of the oxygen-hydrogen mixture, the reaction of the ion exchange in aqueous solution), the second - quickly (combustion of substances, the interaction of zinc with acid), the third is slow (iron rusting, rotting organic residues). There are so slow reactions that the person simply cannot see them. For example, the transformation of granite in sand and clay occurs over thousands of years.

In other words, chemical reactions can flow with different speed.

But what is speed reaction? What is the exact definition of this value and, most importantly, its mathematical expression?

The reaction rate is called a change in the amount of substance per unit of time in one unit of volume. Mathematically, this expression is written as:

Where n. 1 andn. 2 - the amount of substance (mole) at time t 1 and t 2, respectively, in the system volume V..

What sign plus or minus (±) will stand before expressing speed depends on the change in the number of which substances we look - the product or reagent.

It is obvious that during the reaction there is a consumption of reagents, that is, their number decreases, therefore, for reagents, the expression (N 2 - N 1) always matters less than zero. Since the speed cannot be a negative value, in this case before the expression you need to put a "minus" sign.

If we look at changing the amount of product, not a reagent, then before the expression for calculating the speed sign "minus" is not required, since the expression (N 2 - N 1) is always positive in this case, because The amount of product as a result of the reaction can only increase.

The ratio of the amount of substance n. To the volume in which this amount of substance is called the molar concentration FROM:

Thus, using the concept of molar concentration and its mathematical expression, you can write another option for determining the reaction speed:

The reaction rate is called the change in the molar concentration of the substance as a result of the flow of a chemical reaction for one time unit:

Factors affecting the reaction rate

It is often extremely important to know from which the speed of one or another reaction depends and how to influence it. For example, the oil refining industry literally beats for each additional half-circuit of the product per unit of time. After all, given the enormous amount of oil processed, even half apler flows into a major financial annual profit. In some cases, it is extremely important to slow down any reaction, in particular corrosion of metals.

So what does the reaction rate depend on? It depends, oddly enough, from many different parameters.

In order to understand this issue, first of all, let us imagine what happens as a result of a chemical reaction, for example:

A + B → C + D

The equation written above reflects the process in which molecules of substances A and B, facing each other, form molecules of substances C and D.

That is, undoubtedly, in order for the reaction to pass, at least, it is necessary to collide the molecules of the starting materials. Obviously, if we increase the amount of molecules in a unit of volume, the number of collisions will increase in the same way as the frequency of your collisions with passengers in a crowded bus will increase compared to the semi-empty.

In other words, the reaction rate increases with increasing concentration of reacting substances.

In the case when one of the reagents or several are immediately gases, the reaction rate increases with the increase in pressure, since the gas pressure is always directly proportional to the concentration of its molecules.

However, the collision of particles is necessary, but not at all in sufficient condition of the reaction. The fact is that according to the calculations, the number of collisions of molecules of reacting substances at their reasonable concentration is so large that all reactions should flow in an instant. However, in practice it does not happen. What is the matter?

The fact is that not all collision of the reagents molecules will necessarily be effective. Many collisions are elastic - molecules bounce apart from each other like balls. In order for the reaction to pass, molecules must have sufficient kinetic energy. The minimum energy to which molecules of the reacting substances should have to ensure that the reaction passes is called the activation energy and is indicated as e a. In a system consisting of a large number of molecules, there is a distribution of energy molecules, some of them have low energy, part high and middle. Of all these molecules, only a small part of the energy molecules exceeds the activation energy.

As is known from the course of physics, the temperature in fact is the measure of the kinetic energy of the particles, of which the substance consists. That is, the faster the particles are moving, the component of the substance, the higher its temperature. Thus, it is obviously increasing the temperature in fact, we increase the kinetic energy of molecules, as a result of which the proportion of molecules with an energy exceeding E A and their collision will lead to a chemical reaction.

The fact of the positive effect of the temperature on the rate of flow of reaction back in the 19th century empirically set the Dutch chemist Vant Hoff. Based on the studies held by him, he formulated the rule that still carries his name, and it sounds as follows:

The rate of any chemical reaction increases 2-4 times with an increase in temperature by 10 degrees.

Mathematical display of this rule is written as:

where V. 2 and V. 1 - Speed \u200b\u200bat a temperature T 2 and T 1, respectively, and γ is the temperature coefficient of the reaction, the value of which most often lies in the range from 2 to 4.

Often the speed of many reactions can be enhanced using catalysts.

Catalysts - substances accelerating any reaction and are not consistent.

But how does the catalyst manage to increase the reaction rate?

Recall the activation energy E a. Molecules with energy are less than activation energy in the absence of a catalyst can not interact with each other. Catalysts, change the path through which the reaction flows is just as an experienced conductor will pave the expedition route not directly through the mountain, but with the help of a bypass trail, with the result that even those satellites that did not have enough energy to climb the mountain will be able to move to another Her side.

Despite the fact that the catalyst is not spent during the reaction, nevertheless it takes an active part in it, forming intermediate compounds with reagents, but by the end of the reaction returns to its original state.

In addition to the above factors affecting the reaction rate, if there is a separation boundary (heterogeneous reaction) between the reactors, the reaction rate will depend on the area of \u200b\u200bcontact of the reagents. For example, imagine a granule of metal aluminum, which was thrown into the tube with an aqueous solution of hydrochloric acid. Aluminum is an active metal that is able to react with acids with non-oxidants. With hydrochloric acid, the reaction equation is as follows:

2Al + 6HCl → 2AlCl 3 + 3H 2

Aluminum is a solid, and this means that the reaction with hydrochloric acid goes only on its surface. Obviously, if we increase the surface area, after having rolled the aluminum granules in Foil, we thereby provide a greater number of aluminum atoms available for the reaction with acid. As a result, the reaction rate will increase. Similarly, the increase in the surface of the solid can be achieved by grinding it into powder.

Also, the speed of the heterogeneous reaction, in which the solid reacts with gaseous or liquid reacts, often has a positive effect, which is due to the fact that, as a result of the mixing, removal from the reaction zone accumulating molecules of reaction products is achieved and the new portion of the reagent molecules is reached.

The latter should also be noted a huge effect on the rate of reaction and the nature of reagents. For example, the lower in the Mendeleev table there is an alkaline metal, the faster it reacts with water, the fluorine among all halogen reacts the most quickly with gaseous hydrogen, etc.

Summarizing all of the above, the reaction rate depends on the following factors:

1) Concentration of reagents: the higher, the greater the reaction rate

2) Temperature: with increasing temperature The speed of any reaction increases

3) the area of \u200b\u200bcontact of the reactant substances: the larger the area of \u200b\u200bcontact of the reagents, the higher the reaction rate

4) Stirring if the reaction occurs honey with solid substance and liquid or gas mixing can speed it up.

The mechanisms of leakage of chemical transformations and their speed studies the chemical kinetics. Chemical processes occur in time with different speeds. Some happening quickly, almost instantly, it takes a very long time for the flow of others.

Speed \u200b\u200breaction - The rate of which reagents is consumed (their concentration is reduced) or the reaction products are formed in a unit of volume.

Factors that can affect the rate of chemical reaction

To how fast chemical interaction will occur, the following factors may affect:

• concentration of substances;
• the nature of reagents;
• temperature;
• the presence of the catalyst;
• pressure (for reactions in the gas environment).

Thus, changing certain conditions for the flow of the chemical process, it is possible to affect how quickly the process will flow.

In the process of chemical interaction, the particles of reacting substances are faced with each other. The number of such coincidences is proportional to the number of particles of substances in the volume of the reacting mixture, and therefore proportionately molar concentrations of reagents.

The law of acting masses Describes the dependence of the reaction rate from the molar concentrations of substances entering into interaction.

For an elementary reaction (A + V → ...), this law is expressed by the formula:

υ \u003d k ∙ with a ∙ s b,

where k is a speed constant; C A and C B - molar concentrations of reagents, A and V.

If one of the reactors is in a solid state, the interaction occurs on the surface of the phase partition, in connection with this, the concentration of the solid substance is not included in the equation of the kinetic law of the existing mass. To understand the physical meaning of the velocity constant, it is necessary to accept C, A and C equal to 1. Then it becomes clear that the rate constant is equal to the reaction rate at concentrations of reagents equal to one.

Nature reagents

Since the chemical bonds of reacting substances are destroyed in the process of interaction and new bonds of the reaction products are formed, the nature of the connections participating in the reaction of compounds and the structure of the reacting substances molecules will be played.

Surface surface of the contact of reagents

This characteristic as the surface area of \u200b\u200bthe surface of solid reagents is affected by the reaction, sometimes quite significantly. Grinding a solid substance allows you to increase the surface area of \u200b\u200bthe contact of the reagents, and therefore accelerate the course of the process. The area of \u200b\u200bcontact of soluble substances is easily increased by dissolving the substance.

Reaction temperature

With increasing temperature, the energy of the encountered particles will increase, it is obvious that with increasing temperature and the chemical process will be accelerated. A visual example of how the increase in temperature affects the process of interaction of substances, you can read the data given in the table.

Table 1. Effect of temperature change on the water formation rate (O 2 + 2N 2 → 2N 2 O)

For a quantitative description of how the temperature can affect the rate of interaction of the substances use the Vant-Gooff rule. The Vant-Hoffa rule is that with an increase in temperature by 10 degrees, acceleration occurs 2-4 times.

The mathematical formula describing the Vant-Gooff rule is as follows:

Where γ is the temperature coefficient of the chemical reaction rate (γ \u003d 2-4).

But much more accurately describes the temperature dependence of the velocity constant Equation of Arrhenius:

Where R is a universal gas constant, A is a multiplier determined by the reaction, E, A - activation energy.

The activation energy is called such an energy that molecule must acquire, so that the chemical transformation occur. That is, it is a kind of energy barrier, which will be necessary to overcome molecules encountered in the reaction volume to redistribute connections.

The activation energy does not depend on external factors, and depends on the nature of the substance. The value of activation energy up to 40 - 50 kJ / mol allows substances to respond with each other quite actively. If activation energy exceeds 120 kJ / molThe substances (at normal temperatures) will react very slowly. The change in temperature leads to a change in the number of active molecules, that is, molecules that have reached the energy greater than the activation energy, which means that are capable of chemical transformations.

Catalyst action

The catalyst is called a substance capable of accelerating the process, but not part of its products. Catalysis (acceleration of chemical transformation) is separated by · homogeneous, · heterogeneous. If reagents and catalyst are in the same aggregate states, the catalysis is called homogeneous, if in various, then heterogeneous. The mechanisms of the action of catalysts are diverse and quite complex. In addition, it is worth noting that the selection of action is characterized by catalysts. That is, the same catalyst, accelerating one reaction, may not change the speed of the other.

Pressure

If gaseous substances are involved in the transformation, then the process of pressure changes in the system will influence the process rate . This is becauseThat for gaseous reagents, the change in pressure leads to a change in concentration.

Experimental determination of the speed of the chemical reaction

It is possible to determine the speed of the chemical transformation experimentally, having obtained data on how the concentration of substances entering into the reaction, or products changes per unit of time. Methods for obtaining such data are divided into

• chemical
• physico-chemical.

Chemical methods are quite simple, available and accurate. With their help, the speed is determined, directly measuring the concentration or the amount of substance of reagents or products. In the case of a slow reaction, to control how the reagent is consumed by samples. After that determine the content in the reagent sample. After selecting samples at equal periods of time, it is possible to obtain data on the change in the amount of substance in the process of interaction. Most often use such types of analysis as titrimimetry and gravimetry.

If the reaction proceeds quickly, then to select the sample, it has to be stopped. This can be done by cooling, sharp removal of catalystYou can also dilute or translate one of the reagents to non-reactive state.

Methods of physicochemical analysis in modern experimental kinetics are used more often than chemical. With their help, it is possible to observe the change in the concentrations of substances in real time. At the same time, the reaction is not necessary to stop and select samples.

Physico-chemical methods are based on the measurement of the physical property depending on the quantitative content in the system of a particular connection and varying with time. For example, if gases are involved in the reaction, then this property may be pressure. Also measured electrical conductivity, refractive index, absorption spectra of substances.

Let us define the basic concept of chemical kinetics - the speed of the chemical reaction:

The speed of the chemical reaction is the number of elementary acts of the chemical reaction occurring per unit of time in a unit of volume (for homogeneous reactions) or on a unit of the surface (for heterogeneous reactions).

The speed of the chemical reaction is a change in the concentration of reactant substances per unit of time.

The first definition is the most stringent; It follows from it that the speed of the chemical reaction can also be expressed as a change in the time of any parameter of the state of the system, depending on the number of particles of any reactive substance, assigned to a unit of volume or surface - electrical conductivity, optical density, dielectric constant, etc. etc. However, the dependence of the concentration of reagents on time is considered most often in chemistry. In the case of unilateral (irreversible) chemical reactions (here, only one-sided reactions are considered) it is obvious that the concentrations of the initial substances in time are constantly decreasing (ΔC is< 0), а концентрации продуктов реакции увеличиваются (ΔС прод > 0). The reaction rate is considered positive, so mathematically definition middle reaction speed In the time interval ΔT is written as follows:

(II.1)

At various time intervals, the average rate of chemical reaction has different values; true (instant) reaction rate Determined as a derivative of the time concentration:

(II.2)

The graphic image of the concentration of reagents from time to time is kinetic curve (Figure 2.1).

Fig. 2.1 Kinetic curves for starting materials (A) and reaction products (B).

The true reaction rate can be determined graphically by having a tangent of kinetic curve (Fig. 2.2); The true reaction rate is currently equal to the absolute value of tangent tangential angle:

Fig. 2.2 Graphic definition of V East.

(II.3)

It should be noted that in the event that the stoichiometric coefficients in the equation of the chemical reaction of the unequal, the value of the reaction will depend on whether the concentration of which reagent is determined. Obviously, in the reaction

2N 2 + O 2 → 2N 2

the concentrations of hydrogen, oxygen and water change to varying degrees:

ΔC (H 2) \u003d ΔC (H 2 O) \u003d 2 ΔC (O 2).

The speed of the chemical reaction depends on the set of factors: the nature of the reactant substances, their concentration, temperature, the nature of the solvent, etc.

One of the tasks facing the chemical kinetics is the determination of the composition of the reaction mixture (that is, the concentrations of all reagents) at any time, for which it is necessary to know the dependence of the reaction rate from concentrations. In general, the greater the concentration of reacting substances, the greater the speed of the chemical reaction. At the heart of chemical kinetics lies t. N. the main postulate of chemical kinetics:

The chemical reaction rate is directly proportional to the product of the concentrations of the reactants taken in some degrees.

That is for reaction

AA + BB + DD + ... → It + ...

Can be recorded

(II.4)

The ratio of the proportionality of K is chemical Reaction Speed \u200b\u200bConstant. The rate constant is numerically equal to the reaction rate at concentrations of all reactants equal to 1 mol / l.

The dependence of the reaction rate on the concentrations of the reactant substances is determined experimentally and is called kinetic equation Chemical reaction. Obviously, in order to record the kinetic equation, it is necessary to experimentally determine the amount of the rate constant and indicators of the degree at the concentrations of reactant substances. An indicator of the degree at the concentration of each of the reactants in the kinetic equation of a chemical reaction (in equation (II.4), respectively, X, Y and Z) is private reaction order on this component. The amount of degree indicators in the kinetic equation of the chemical reaction (X + Y + Z) is general reaction procedure . It should be emphasized that the reaction procedure is determined only from the experimental data and is not associated with stoichiometric coefficients at reagents in the reaction equation. The stoichiometric equation of the reaction is the equation of material balance and in no way can determine the nature of the flow of this reaction in time.

In the chemical kinetics, it is customary to classify the reaction in the amount of the total reaction. Consider the dependence of the concentration of reacting substances on time for irreversible (unilateral) reactions of zero, first and second orders.

Kinetics- Science of chemical reaction speeds.

Chemical reaction rate- the number of elementary acts of chemical interaction flowing into a unit of time per unit volume (homogeneous) or on a unit of surface (heterogeneous).

True reaction rate:

For homogeneous, heterogeneous reactions:

1) concentration of reacting substances;

2) temperature;

3) catalyst;

4) inhibitor.

Only for heterogeneous:

1) the rate of supply of reaction substances to the surface of the phase section;

2) Surface area.

The main factor is the nature of the reactant substances - the nature of the connection between atoms in the reagent molecules.

NO 2 - nitrogen oxide (IV) - lisus tail, CO - carbon monoxide, carbon monoxide.

If they oxidize them, then in the first case the reaction will go instantly, it is necessary to open the vessel plug, in the second case, the reaction is stretched over time.

The concentration of reacting substances will be discussed below.

Blue opalescence indicates the moment of sulfur falling, the higher the concentration, the speed above.

Fig. 10

The greater the concentration of Na 2 S 2 O 3, the less time the reaction is. On the graph (Fig. 10) shows directly proportional dependence. The quantitative dependence of the reaction rate on the concentration of the reactant substances is expressed by ZDM (the law of the active masses), which states: the rate of chemical reaction is directly proportional to the product of the concentrations of reacting substances.

So, the main law of kineticsit is an experienced law: the reaction rate is proportional to the concentration of reactant substances, an example: (i.e., for the reaction)

For this reaction, H 2 + J 2 \u003d 2NJ - the speed can be expressed through a change in the concentration of any of the substances. If the reaction proceeds from left to right, the concentration H 2 and J 2 will decrease, the concentration of HJ is to increase along the reaction. For instant reaction speed, you can record the expression:

square brackets denotes a concentration.

Physical meaning k-molecules are in continuous motion, faced, scatter, hit the wall of the vessel. In order to occur in the chemical reaction of the NJ formation, H 2 and J 2 molecules must be encountered. The number of such collisions will be the greater, the more the molecules H 2 and J 2 are contained in the volume, that is, the greater the values \u200b\u200b[H 2] and. But molecules are moving at different speeds, and the total kinetic energy of two facing molecules will be different. If the fastest H 2 and J 2 molecules are encountered, their energy may be so large that the molecules are separated by iodine and hydrogen atoms, flying and interacting with other molecules H 2 + J 2 > 2H + 2J, then it will be H + J 2 > HJ + J. If the energy of the colliding molecules is less, but quite large for the weakening of the bonds H - H and J - J, the formation of iodorodor formation will occur:

Most of the same encountered energy molecules are less necessary for weakening bonds in H 2 and J 2. Such molecules "quietly" will face and also "quietly" will disperse, remaining the fact that they were, H 2 and J 2. Thus, not everything, but only a part of the collisions leads to a chemical reaction. The proportionality coefficient (k) shows the number of the results resulting in the reaction of collisions at concentrations [H 2] \u003d \u003d 1mol. Value k-const speed. How can the speed be permanent? Yes, the speed of uniform rectilinear movement is called a constant vector magnitude equal to the ratio of body movement for any period of time to the value of this gap. But molecules are moving chaotic, where can there be speed - const? But the constant speed can only be at a constant temperature. With increasing temperature, the proportion of fast molecules increases, the collisions of which lead to the reaction, i.e. the speed constant increases. But the increase in speed constant is not limitless. At some temperature, the energy of molecules will become so large that almost all the collisions of the reagents will be effective. When a collision of two rapid molecules will occur the reverse reaction.

There will be such a moment when the rate of formation 2NJ of H 2 and J 2 and the decomposition will be equal, but this is already a chemical equilibrium. The dependence of the reaction rate on the concentration of reactant substances can be traced using the traditional reaction of the interaction of sodium thiosulfate solution with sulfuric acid solution.

Na 2 S 2 O 3 + H 2 SO 4 \u003d Na 2 SO 4 + H 2 S 2 O 3, (1)

H 2 S 2 O 3 \u003d SV + H 2 O + SO 2 ^. (2)

The reaction (1) proceeds almost instantly. The reaction rate (2) depends on a constant temperature from the concentration of the reactant H 2 S 2 O 3. It is this reaction that we observed - in this case, the speed is measured by time from the beginning of draining solutions until opalescence appears. In the article L. M. Kuznetsova the reaction of the interaction of sodium thiosulfate with hydrochloric acid is described. She writes that when pluming solutions, opalescence (clouded) occurs. But this statement L. M. Kuznetsova is mistakenly so as opalescence and clouding are different things. Opalacementation (from opal and latin escentia.- suffix, meaning a weak action) - the scattering of light with turwind media due to their optical inhomogeneity. Light scattering- Deviation of light rays propagating in the medium in all directions from the initial direction. Colloid particles are able to dissipate the light (the effect of the tyndal - Faraday) - this explains the opalescence, the light moonliness of the colloidal solution. When carrying out this experience, it is necessary to take into account the blue opalescence, and then coagulation of the colloidal sulfur suspension. The same density of the suspension is noted according to the apparent disappearance of any figure (for example, mesh at the bottom of the cup), observed from above through a solution layer. Time is counted in the stopwatch from the moment of draining.

Solutions Na 2 S 2 O 3 x 5H 2 O and H 2 SO 4.

The first is prepared by dissolving 7.5 g of salts in 100 ml of H 2 O, which corresponds to 0.3 m concentration. To prepare the solution H 2 SO 4 of the same concentration, it is necessary to measure 1.8 ml of H 2 SO 4 (K), ? = = 1.84 g / cm 3 and dissolve it in 120 ml H 2 O. Prepared solution Na 2 S 2 O 3 Pour into three glasses: in the first - 60 ml, in the second - 30 ml, in the third - 10 ml. In the second glass, add 30 ml of H 2 O distilled, and in the third - 50 ml. Thus, in all three glasses it will be 60 ml of liquid, but in the first salt concentration conditionally \u003d 1, in the second - ѕ, and in the third - 1/6. After the solutions are prepared, in the first glass with a salt solution, with a solution of salt 60 ml of solution H 2 SO 4 and turn on the stopwatch, etc. Considering that the reaction rate drops with diluting the solution Na 2 S 2 O 3, it can be determined as a magnitude, back proportional time v \u003d.one/? and build a graph, postponing on the abscissa axis concentration, and on the axis ordinate - the reaction rate. From this pin - the reaction rate depends on the concentration of substances. The data obtained are listed in Table 3. You can perform this experience with the help of a burette, but it requires that performing great practices, because the schedule is incorrect.

Table 3.

Speed \u200b\u200band reaction time

The law of Guldberg-Vaiga is confirmed - Professor of Chemistry Gulderg and a young scientist Vaug).

Consider the following factor - temperature.

With increasing temperature, the speed of most chemical reactions increases. This dependence is described by the Vant-Gooff Rule: "With an increase in temperature for every 10 ° C, the speed of chemical reactions increases 2 to 4 times."

where ? – the temperature coefficient showing how many times the reaction rate increases with an increase in temperature by 10 ° C;

v. 1 - reaction rate at temperatures t 1;

v 2 -reaction rate at temperatures t 2.

For example, the reaction at 50 ° C flows in two minutes, how long will the process end at 70 ° C if the temperature coefficient ? = 2?

t 1 \u003d.120 C \u003d 2 min; t 1 \u003d.50 ° C; t 2 \u003d.70 ° С.

Even a slight increase in temperature causes a sharp increase in the reaction rate of the active collisions of the molecule. According to the theory of activation, only those molecules are involved in the process, the energy of which is more than the average energy of molecules to a certain value. This excess energy is activation energy. Its physical meaning is that energy that is necessary for an active clash of molecules (restructuring orbitals). The number of active particles, and consequently, the reaction rate increases with the temperature according to the exponential law, according to the Arrhenius equation, reflecting the dependence of the temperature velocity constant

where BUT -arrhenius proportionality coefficient;

k-boltzmann's constant;

E A -activation energy;

R -gas constant;

T-temperature.

The catalyst is a substance that accelerates the reaction rate that is not consumed by itself.

Catalysis- phenomenon change the reaction rate in the presence of a catalyst. Distinguish homogeneous and heterogeneous catalysis. Homogeneous- If reagents and catalyst are in one aggregate state. Heterogeneous- If reagents and catalyst in various aggregate states. For catalysis, see separately (on).

Inhibitor- substance that slows down the reaction rate.

The following factor is the surface area. The greater the surface of the reactant, the greater the speed. Consider on the example the effect of the degree of dispersion on the reaction rate.

Caco 3 - marble. Tile marble is lowered in HCl hydrochloric acid, wait five minutes, it will dissolve completely.

Powdered marble - with it I will do the same procedure, it dissolved in thirty seconds.

The equation of both processes is equally.

CaCo 3 (TV) + HCl (g) \u003d CaCl 2 (TV) + H 2 O (g) + CO 2 (g) ^.

So, when adding a powdered marble, the time is less than when adding tiled marble, with the same mass.

With an increase in the surface of the phase section, the speed of heterogeneous reactions increases.