In life, we are faced with different chemical reactions. Some of them, like iron rusting, can take several years. Others, such as fermenting sugar into alcohol, takes several weeks. Firewood in the stove burns out in a couple of hours, and gasoline in the engine in a split second.
To reduce equipment costs, chemical plants increase the rate of reactions. And some processes, for example, food spoilage, metal corrosion, need to be slowed down.
Chemical reaction rate can be expressed as change in the amount of substance (n, modulo) per unit of time (t) - compare the speed of a moving body in physics as a change in coordinates per unit of time: υ \u003d Δx / Δt. So that the speed does not depend on the volume of the vessel in which the reaction is taking place, we divide the expression by the volume of the reacting substances (v), i.e., we obtainchange in the amount of substance per unit of time per unit of volume, or change in the concentration of one of the substances per unit of time:
n 2 - n 1 Δn
υ = –––––––––– = –––––––– \u003d Δс / Δt (1)
(t 2 - t 1) v Δt v
where c \u003d n / v is the concentration of the substance,
Δ (read "delta") is the generally accepted designation for the change in value.
If substances have different coefficients in the equation, the reaction rate for each of them, calculated using this formula, will be different. For example, 2 moles of sulfur dioxide reacted completely with 1 mole of oxygen in 10 seconds in 1 liter:
2SO 2 + O 2 \u003d 2SO 3
The oxygen rate will be: υ \u003d 1: (10 1) \u003d 0.1 mol / l s
Sulfurous gas speed: υ \u003d 2: (10 1) \u003d 0.2 mol / l · s - this does not need to be memorized and said in the exam, an example is given in order not to get confused if this question arises.
The rate of heterogeneous reactions (involving solids) is often expressed per unit area of \u200b\u200bthe contacting surfaces:
Δn
υ \u003d –––––– (2)
Δt S
Reactions are called heterogeneous when the reacting substances are in different phases:
- a solid with another solid, liquid or gas,
- two immiscible liquids,
- liquid with gas.
Homogeneous reactions occur between substances in one phase:
- between well miscible liquids,
- gases
- substances in solutions.
Conditions affecting the rate of chemical reactions
1) The reaction speed depends on nature of reactants... Simply put, different substances react at different rates. For example, zinc reacts violently with hydrochloric acid, and iron rather slowly.
2) The reaction speed is the greater, the higher concentration substances. With a highly diluted acid, zinc will react much longer.
3) The reaction rate increases significantly with increasing temperature... For example, to burn fuel, it is necessary to ignite it, i.e. increase the temperature. For many reactions, an increase in temperature by 10 ° C is accompanied by a 2–4-fold increase in the rate.
4) Speed heterogeneous reactions increase with increasing surfaces of reactants... Solids are usually ground for this. For example, in order for iron and sulfur powders to react when heated, the iron must be in the form of fine sawdust.
Please note that formula (1) is implied in this case! Formula (2) expresses the speed per unit area, therefore it cannot depend on the area.
5) The reaction rate depends on the presence of catalysts or inhibitors.
Catalysts - substances that accelerate chemical reactions, but are not consumed themselves. An example is the violent decomposition of hydrogen peroxide with the addition of a catalyst - manganese (IV) oxide:
2H 2 O 2 \u003d 2H 2 O + O 2
Manganese (IV) oxide remains at the bottom and can be reused.
Inhibitors - substances that slow down the reaction. For example, corrosion inhibitors are added to the hot water heating system to extend the life of pipes and radiators. In cars, corrosion inhibitors are added to brake and coolant.
A few more examples.
Purpose of work: study of the rate of a chemical reaction and its dependence on various factors: the nature of the reacting substances, concentration, temperature.
Chemical reactions take place at different rates. The rate of chemical reaction called the change in the concentration of the reactant per unit time. It is equal to the number of interactions per unit time per unit volume for a reaction proceeding in a homogeneous system (for homogeneous reactions), or per unit interface for reactions proceeding in a heterogeneous system (for heterogeneous reactions).
Average reaction rate v Wed ... in the time interval from t 1 before t 2 defined by the relationship:
where C 1 and C 2 - molar concentration of any participant in the reaction at times t 1 and t 2 respectively.
The sign “-“ before the fraction refers to the concentration of the starting substances, Δ FROM < 0, знак “+” – к концентрации продуктов реакции, ΔFROM > 0.
The main factors affecting the rate of a chemical reaction: the nature of the reacting substances, their concentration, pressure (if gases are involved in the reaction), temperature, catalyst, interface area for heterogeneous reactions.
Most chemical reactions are complex processes that take place in several stages, i.e. consisting of several elementary processes. Elementary or simple reactions are reactions that take place in one stage.
For elementary reactions, the dependence of the reaction rate on concentration is expressed by the law of mass action.
At a constant temperature, the rate of a chemical reaction is directly proportional to the product of the concentrations of the reactants, taken in powers equal to the stoichiometric coefficients.
For the reaction in general
a A + b B ... → c C,
according to the law of mass action v expressed by the ratio
v \u003d K ∙ s (A) a ∙ s (B) b,
where s (A) and c (B) - molar concentrations of reactants A and B;
TO Is the rate constant of this reaction, equal to v, if a s (A) a \u003d 1 and c (B) b \u003d 1, and depending on the nature of the reacting substances, temperature, catalyst, interface area for heterogeneous reactions.
The expression of the dependence of the reaction rate on concentration is called the kinetic equation.
In the case of complex reactions, the law of mass action is applicable to each individual stage.
For heterogeneous reactions, the kinetic equation includes only the concentrations of gaseous and dissolved substances; so, for coal burning
C (c) + O 2 (g) → CO 2 (g)
the velocity equation has the form
v \u003d K ∙ s (O 2)
A few words about molecularity and kinetic order of the reaction.
Concept "Reaction molecularity" apply only to simple reactions. Molecularity of the reaction characterizes the number of particles participating in the elementary interaction.
Distinguish between mono-, bi- and trimolecular reactions, in which one, two and three particles participate, respectively. The probability of a simultaneous collision of three particles is small. The elementary process of interaction of more than three particles is unknown. Examples of elementary reactions:
N 2 O 5 → NO + NO + O 2 (monomolecular)
H 2 + I 2 → 2HI (bimolecular)
2NO + Cl 2 → 2NOCl (trimolecular)
The molecularity of simple reactions coincides with the general kinetic order of the reaction. The order of the reaction determines the nature of the dependence of the rate on concentration.
The general (total) kinetic order of the reaction is the sum of the exponents at the concentrations of reactants in the reaction rate equation, determined experimentally.
As the temperature rises, the rate of most chemical reactions increases. The dependence of the reaction rate on temperature is approximately determined by the Van't Hoff rule.
With an increase in temperature for every 10 degrees, the rate of most reactions increases by 2-4 times.
where and are the reaction rate, respectively, at temperatures t 2 and t 1 (t 2\u003e t 1);
γ is the temperature coefficient of the reaction rate, this is a number showing how many times the rate of a chemical reaction increases with an increase in temperature by 10 0.
Using the Van't Hoff rule, it is only possible to roughly estimate the effect of temperature on the reaction rate. A more accurate description of the temperature dependence of the reaction rate is feasible within the framework of the Arrhenius activation theory.
One of the methods of accelerating a chemical reaction is catalysis, which is carried out with the help of substances (catalysts).
Catalysts - these are substances that change the rate of a chemical reaction due to repeated participation in an intermediate chemical interaction with the reaction reagents, but after each cycle of intermediate interaction restore their chemical composition.
The mechanism of action of the catalyst is reduced to a decrease in the value of the activation energy of the reaction, i.e. a decrease in the difference between the average energy of active molecules (active complex) and the average energy of molecules of the starting substances. In this case, the rate of the chemical reaction increases.
7.1. Homogeneous and heterogeneous reactions
Chemicals can be in different states of aggregation, while their chemical properties in different states are the same, but the activity is different (which was shown in the last lecture using the example of the thermal effect of a chemical reaction).
Consider various combinations of aggregate states in which two substances A and B.
A (g), B (g) |
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A (tv.), B (tv.) | A (f.), B (tv.) | mingle | A (tv.), B (g.) | A (f.), B (g.) |
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mingle | (solution) | |||||||||||||||||||||||||||||
heterogeneous | heterogeneous | heterogeneous | homogeneous | heterogeneous | heterogeneous | homogeneous |
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Hg (f) + HNO3 | H2 O + D2 O | Fe + O2 | H2 S + H2 SO4 | CO + O2 |
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A phase is a region of a chemical system within which all properties of the system are constant (identical) or continuously change from point to point. Separate phases are each of the solids, in addition there are phases of solution and gas.
Homogeneous is called chemical system, in which all substances are in one phase (in solution or in gas). If there are several phases, then the system is called
heterogeneous.
Respectively chemical reactionis called homogeneous if the reagents are in the same phase. If the reagents are in different phases, then chemical reactioncalled heterogeneous.
It is easy to understand that since a chemical reaction requires contact of reagents, a homogeneous reaction occurs simultaneously in the entire volume of a solution or reaction vessel, while a heterogeneous reaction occurs at a narrow interface between phases - at the interface. Thus, a purely theoretical homogeneous reaction occurs faster than a heterogeneous one.
Thus, we move on to the concept chemical reaction rate.
Chemical reaction rate. The law of the acting masses. Chemical equilibrium.
7.2. Chemical reaction rate
The section of chemistry that studies the rates and mechanisms of chemical reactions is the section of physical chemistry and is called chemical kinetics.
The rate of chemical reactionis the change in the amount of substance per unit time per unit volume of the reacting system (for a homogeneous reaction) or per unit surface area (for a heterogeneous reaction).
Thus, if the volume | or area | interface |
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do not change, then the expressions for the rates of chemical reactions have the form: |
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hom o | |||||||||||
The ratio of the change in the amount of a substance to the volume of the system can be interpreted as a change in the concentration of a given substance.
Note that for reagents, the expression for the rate of a chemical reaction is written with a minus sign, since the concentration of reagents decreases, and the rate of a chemical reaction is generally positive.
Further conclusions are based on simple physical considerations that consider a chemical reaction as a consequence of the interaction of several particles.
Elementary (or simple) is a chemical reaction that occurs in one stage. If there are several stages, then such reactions are called complex, or compound, or gross reactions.
In 1867, to describe the rate of a chemical reaction was proposed law of mass action: rate of an elementary chemical reaction proportional to the concentrations of reactants in powers of stoichiometric coefficients n A + m B P,
A, B - reagents, P - products, n, m - coefficients.
W \u003d k n m
The coefficient k is called the rate constant of a chemical reaction,
characterizes the nature of interacting particles and does not depend on the concentration of particles.
Chemical reaction rate. The law of the acting masses. Chemical equilibrium. The quantities n and m are called order of reaction by substanceA and B, respectively, and
their sum (n + m) - order of reaction.
For elementary reactions, the reaction order can be 1, 2 and 3.
Elementary reactions with order 1 are called monomolecular, with order 2 - bimolecular, with order 3 - trimolecular in terms of the number of molecules involved. Elementary reactions above the third order are unknown - calculations show that the simultaneous meeting of four molecules at one point is too incredible an event.
Since a complex reaction consists of a certain sequence of elementary reactions, its rate can be expressed in terms of the rates of individual stages of the reaction. Therefore, for complex reactions, the order can be any, including fractional or zero (the zero order of the reaction indicates that the reaction occurs at a constant rate and does not depend on the concentration of the reacting particles W \u003d k).
The slowest of the stages of a complex process is usually called the rate-limiting stage (rate-limiting stage).
Imagine that a large number of molecules went to a free movie theater, but there is a controller at the entrance who checks the age of each molecule. Therefore, a stream of matter enters the doors of the cinema, and the molecules penetrate into the cinema hall one by one, i.e. very slow.
Examples of elementary first-order reactions are processes of thermal or radioactive decay, respectively, the rate constant k characterizes either the probability of breaking a chemical bond, or the probability of decay per unit time.
There are a lot of examples of elementary second-order reactions - this is the most familiar way of reaction flow - particle A bumped into particle B, some kind of transformation happened and something happened there (note that the products in theory do not affect anything - all attention only the reacting particles).
On the contrary, there are quite a few elementary reactions of the third order, since it is rather rare for three particles to meet simultaneously.
As an illustration, consider the predictive power of chemical kinetics.
Chemical reaction rate. The law of the acting masses. Chemical equilibrium.
First order kinetic equation
(illustrative additional material)
Consider a homogeneous first-order reaction, the rate constant of which is equal to k, the initial concentration of substance A is equal to [A] 0.
By definition, the rate of a homogeneous chemical reaction is |
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K [A] | concentration change per unit time. Times substance A - |
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reagent, put a minus sign. | ||||||||||||||||||
Such an equation is called differential (there is |
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derivative) | ||||||||||||||||||
[A] | To solve it, we transfer the quantities to the left side |
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concentration, and on the right - time. | ||||||||||||||||||
If the derivatives of two functions are equal, then the functions themselves |
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must differ by no more than a constant. | ||||||||||||||||||
To solve this equation, take the integral of the left-hand side (over |
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concentration) and the right side (in time). In order not to frighten |
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ln [A] \u003d −kt + C | listeners, we confine ourselves to the answer. | |||||||||||||||||
The ln sign is the natural logarithm, i.e. number b such that | ||||||||||||||||||
\u003d [A], e \u003d 2.71828 ... | ||||||||||||||||||
ln [A] - ln0 \u003d - kt | The constant C is found from the initial conditions: | |||||||||||||||||
at t \u003d 0, the initial concentration is [A] 0 | ||||||||||||||||||
[A] | Logarithm times - | this is the power of the number, we use the properties of the powers |
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[A] 0 | e a− b \u003d | |||||||||||||||||
Now let's get rid of the opposite logarithm (see the definition |
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logarithm 6-7 lines higher), | why will we raise the number | |||||||||||||||||
to the power of the left side of the equation and the right side of the equation. | ||||||||||||||||||
[A] | E - kt | Multiply by [A] 0 | ||||||||||||||||
[A] 0 | ||||||||||||||||||
First order kinetic equation. | ||||||||||||||||||
[A] \u003d 0 × e - kt | Based | the obtained kinetic equation of the first |
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order can | calculated | concentration of matter | ||||||||||||||||
at any given time | ||||||||||||||||||
For the purposes of our course, this conclusion is for informational purposes, in order to demonstrate to you the use of the mathematical apparatus for calculating the course of a chemical reaction. Therefore, a competent chemist cannot but know mathematics. Learn math!
Chemical reaction rate. The law of the acting masses. Chemical equilibrium. The graph of the dependence of the concentration of reagents and products on time can be qualitatively depicted as follows (using the example of an irreversible first-order reaction)
Factors that affect the reaction rate
1. The nature of the reacting substances
For example, the reaction rate of the following substances: H2 SO4, CH3 COOH, H2 S, CH3 OH - with a hydroxide ion will differ depending on the strength of the H-O bond. To assess the strength of this bond, you can use the value of the relative positive charge on the hydrogen atom: the higher the charge, the easier the reaction will be.
2. Temperature
Life experience tells us that the reaction rate depends on temperature and increases with increasing temperature. For example, milk souring process occurs faster at room temperature, and not in the refrigerator.
Let us turn to the mathematical expression of the law of mass action.
W \u003d k n m
Since the left side of this expression (reaction rate) depends on temperature, therefore, the right side of the expression also depends on temperature. In this case, the concentration, of course, does not depend on temperature: for example, milk retains its fat content of 2.5% both in the refrigerator and at room temperature. Then, as Sherlock Holmes used to say, the remaining solution is correct, no matter how strange it may seem: the rate constant depends on the temperature!
Chemical reaction rate. The law of the acting masses. Chemical equilibrium. The temperature dependence of the reaction rate constant is expressed by means of the Arrhenius equation:
- E a
k \u003d k0 eRT,
wherein
R \u003d 8.314 J mol-1 K-1 - universal gas constant,
E a is the activation energy of the reaction (see below), it is conventionally considered independent of temperature;
k 0 is the preexponential factor (i.e., the factor that comes before the exponential e), the value of which is also almost independent of temperature and is determined, first of all, by the order of the reaction.
Thus, the value of k0 is approximately 1013 s-1 for a first-order reaction, and 10 -10 L mol-1 s-1 for a second-order reaction,
for a third-order reaction - 10 -33 l2 · mol-2 · s-1. It is not necessary to memorize these values.
The exact values \u200b\u200bof k0 for each reaction are determined experimentally.
The concept of activation energy becomes clear from the following figure. In fact, the activation energy is the energy that the reacting particle must have in order for the reaction to take place.
Moreover, if we heat the system, then the energy of the particles increases (dotted graph), while the transition state (≠) remains at the same level. The difference in energy between the transition state and the reactants (activation energy) decreases, and the reaction rate according to the Arrhenius equation increases.
Chemical reaction rate. The law of the acting masses. Chemical equilibrium. In addition to the Arrhenius equation, there is the Van't Hoff equation, which
characterizes the dependence of the reaction rate on temperature by means of the temperature coefficient γ:
The temperature coefficient γ shows how many times the rate of a chemical reaction will increase when the temperature changes by 10o.
Van't Hoff equation:
T 2− T 1
W (T 2) \u003d W (T 1) × γ10
Typically, the γ coefficient is in the range from 2 to 4. For this reason, chemists often use the approximation that an increase in temperature by 20 ° leads to an increase in the reaction rate by an order of magnitude (ie, 10 times).
Chemical reaction rate
Chemical reaction rate - change in the amount of one of the reactants per unit time in a unit of reaction space. Is a key concept in chemical kinetics. The rate of a chemical reaction is always a positive value, therefore, if it is determined by the initial substance (the concentration of which decreases during the reaction), then the resulting value is multiplied by −1.
For example, for a reaction:
the expression for speed will look like this:
... The rate of a chemical reaction at each moment in time is proportional to the concentrations of the reagents, raised to powers equal to their stoichiometric coefficients.For elementary reactions, the exponent at the concentration of each substance is often equal to its stoichiometric coefficient, for complex reactions this rule is not observed. In addition to concentration, the following factors affect the rate of a chemical reaction:
- the nature of the reactants,
- presence of a catalyst,
- temperature (van't Hoff rule),
- pressure,
- the surface area of \u200b\u200bthe reactants.
If we consider the simplest chemical reaction A + B → C, then we will notice that instant the rate of a chemical reaction is variable.
Literature
- Kubasov A.A. Chemical kinetics and catalysis.
- Prigogine I., Defey R. Chemical thermodynamics. Novosibirsk: Nauka, 1966.510 p.
- Yablonsky G.S., Bykov V.I., Gorban A.N., Kinetic Models of Catalytic Reactions, Novosibirsk: Nauka (Siberian Branch), 1983.- 255 p.
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See what "Chemical reaction rate" is in other dictionaries:
RATE OF CHEMICAL REACTION - the basic concept of chemical kinetics. For simple homogeneous reactions, the rate of a chemical reaction is measured by the change in the number of moles of the reacted substance (at a constant volume of the system) or by the change in the concentration of any of the starting substances ... Big Encyclopedic Dictionary
RATE OF CHEMICAL REACTION - the basic concept of chem. kinetics, expressing the ratio of the amount of the reacted substance (in moles) to the time interval for which the interaction took place. Since the concentration of reactants changes during the interaction, the speed usually ... Big Polytechnic Encyclopedia
chemical reaction rate - a value characterizing the intensity of a chemical reaction. The rate of formation of the reaction product is the amount of this product as a result of the reaction per unit of time per unit of volume (if the reaction is homogeneous) or on ... ...
chemical reaction rate - the basic concept of chemical kinetics. For simple homogeneous reactions, the rate of a chemical reaction is measured by the change in the number of moles of the reacted substance (at a constant volume of the system) or by the change in the concentration of any of the starting substances ... encyclopedic Dictionary
Chemical reaction rate - a value that characterizes the intensity of a chemical reaction (see Chemical reactions). The rate of formation of a reaction product is the amount of this product resulting from the reaction per unit of time in a unit of volume (if ... ...
RATE OF CHEMICAL REACTION - main. chemical concept kinetics. For simple homogeneous reactions C. x. R. measured by the change in the number of moles reacted in VA (at constant volume of the system) or by the change in the concentration of any of the initial in B or reaction products (if the volume of the system ...
CHEMICAL REACTION MECHANISM - For complex reactions, consisting of several. stages (simple, or elementary reactions), the mechanism is a set of stages, as a result of which the initial in va are converted into products. Intermediate in you in these reactions can act as molecules, ... ... Natural science. encyclopedic Dictionary
Nucleophilic substitution reactions - (English nucleophilic substitution reaction) substitution reactions, in which the attack is carried out by a nucleophile reagent carrying a lone electron pair. The leaving group in nucleophilic substitution reactions is called a nucleofuge. All ... Wikipedia
Chemical reactions - transformation of some substances into others, different from the original ones in chemical composition or structure. The total number of atoms of each given element, as well as the chemical elements themselves that make up the substance, remain in the chemical composition. unchanged; this R. x ... Great Soviet Encyclopedia
drawing speed - linear speed of metal movement at the exit from the die, m / s. On modern drawing machines, the drawing speed reaches 50 to 80 m / s. However, even when drawing the wire, the speed usually does not exceed 30-40 m / s. When ... ... Encyclopedic Dictionary of Metallurgy
DEFINITION
Chemical kinetics - the doctrine of the rates and mechanisms of chemical reactions.
The study of reaction rates, obtaining data on the factors affecting the rate of a chemical reaction, as well as the study of the mechanisms of chemical reactions are carried out experimentally.
DEFINITION
Chemical reaction rate - change in the concentration of one of the reacting substances or reaction products per unit time with a constant volume of the system.
The rate of homogeneous and heterogeneous reactions is determined differently.
The definition of a measure of the rate of a chemical reaction can be written in mathematical form. Let be the rate of a chemical reaction in a homogeneous system, n B - the number of mole of any of the substances obtained during the reaction, V - the volume of the system, - time. Then in the limit:
This equation can be simplified - the ratio of the amount of substance to volume is the molar concentration of the substance n B / V \u003d \u200b\u200bc B, whence dn B / V \u003d \u200b\u200bdc B and finally:
In practice, the concentration of one or more substances is measured at certain intervals. The concentrations of the starting materials decrease with time, while the concentrations of the products increase (Fig. 1).
Fig. 1. Change in the concentration of the starting substance (a) and the reaction product (b) with time
Factors affecting the rate of a chemical reaction
The factors influencing the rate of a chemical reaction are: the nature of the reacting substances, their concentration, temperature, the presence of catalysts in the system, pressure and volume (in the gas phase).
The effect of concentration on the rate of a chemical reaction is associated with the basic law of chemical kinetics - the law of action of masses (MAS): the rate of a chemical reaction is directly proportional to the product of the concentrations of reactants, raised to the power of their stoichiometric coefficients. ZDM does not take into account the concentration of substances in the solid phase in heterogeneous systems.
For the reaction mA + nB \u003d pC + qD, the mathematical expression of the ZDM will be written:
K × C A m × C B n
K × [A] m × [B] n,
where k is the rate constant of a chemical reaction, which is the rate of a chemical reaction at a concentration of reactants of 1 mol / l. Unlike the rate of a chemical reaction, k does not depend on the concentration of reactants. The higher k, the faster the reaction proceeds.
The dependence of the rate of a chemical reaction on temperature is determined by the Van't Hoff rule. Van't Hoff's rule: every ten degrees the temperature rises, the rate of most chemical reactions increases by about 2 to 4 times. Mathematical expression:
(T 2) \u003d (T 1) × (T2-T1) / 10,
where is the temperature coefficient of Van't Hoff, showing how many times the reaction rate increased with an increase in temperature by 10 o С.
Molecularity and order of reaction
The molecularity of the reaction is determined by the minimum number of molecules simultaneously interacting (participating in an elementary act). Distinguish:
- monomolecular reactions (an example is decomposition reactions)
N 2 O 5 \u003d 2NO 2 + 1 / 2O 2
K × C, -dC / dt \u003d kC
However, not all reactions obeying this equation are monomolecular.
- bimolecular
CH 3 COOH + C 2 H 5 OH \u003d CH 3 COOC 2 H 5 + H 2 O
K × C 1 × C 2, -dC / dt \u003d k × C 1 × C 2
- trimolecular (very rare).
The molecularity of a reaction is determined by its true mechanism. It is impossible to determine its molecularity by writing the reaction equation.
The order of the reaction is determined by the form of the kinetic equation of the reaction. It is equal to the sum of the indicators of the degrees of concentration in this equation. For instance:
CaCO 3 \u003d CaO + CO 2
K × C 1 2 × C 2 - third order
The reaction order can be fractional. In this case, it is determined experimentally. If the reaction proceeds in one stage, then the order of the reaction and its molecularity coincide; if in several stages, then the order is determined by the slowest stage and is equal to the molecularity of this reaction.
Examples of problem solving
EXAMPLE 1
| The task | This reaction proceeds according to the equation 2A + B \u003d 4C. The initial concentration of substance A is 0.15 mol / l, and after 20 seconds - 0.12 mol / l. Calculate the average reaction rate. |
| Decision | Let's write down the formula for calculating the average rate of a chemical reaction: |