Chemical reaction rate. Influence of conditions on the rate of chemical reactions. Catalysis. Topic 3.2

1.

Topic 3.2 Chemical reaction rate. Influence of
conditions on the rate of chemical reactions.
Catalysis
Name of
instructor:M.Azhgaliev

2.

Outline
Introduction
Main part
1.The concept of the rate of chemical reactions
2. Influence of the nature of reactants on the rate of a
chemical reaction
3.Effect of temperature on the rate of chemical reaction
4.Effect of a catalyst on the rate of a chemical reaction
Conclusion
Literature

3.

1.The concept of the rate of chemical
reactions
A branch of chemistry that studies the rate and
mechanisms of chemical reactions - chemical
kinetics.
The rate of a chemical reaction is the change in the
concentration of reactants per unit of time.
For a reaction proceeding according to the equation
A + B = C + D,
the reaction rate can be calculated from the
change in the concentration of one of the reactants,
for example, substance A.

4.

5.

1.The concept of the rate of chemical
reactions
If at time τ1 the concentration of substance A is
equal to C1, and at time τ2 the concentration of
substance A decreased and became equal to C2,
then the rate can be defined as the change in the
concentration of substance A over a period of time.

6.

1.The concept of the rate of chemical
reactions
The rate is positive and the concentration of
the reactants decreases. Therefore, the plusminus sign is generally used in the rate
formula.
C
C f C i
v
1 2

7.

1.The concept of the rate of chemical reactions
The rate of a chemical reaction depends on:
the nature of the reacting substances;
concentration of reactants;
temperature;
the presence of a catalyst.

8.

2.Influence of the nature of reactants on the
rate of a chemical reaction
In aqueous solutions, substances with ionic and
polar covalent bonds interact with great speed.
This is due to the fact that in solutions they form
ions that easily interact with each other.
Example:
silver nitrate in an aqueous solution quickly
reacts with potassium chloride, forming a
precipitate of silver chloride during the ion
exchange reaction:
KCl + AgNO3 = AgCl ↓ + KNO3.

9.

2.Influence of the nature of reactants on the
rate of a chemical reaction
Substances with non-polar and low-polarity
covalent bonds interact at different rates
depending on their chemical activity.
Example:
the reaction of interaction of hydrogen and
fluorine at room temperature proceeds very
quickly (with an explosion):
H2 + F2 = 2HF.
Even when heated, hydrogen and bromine react
slowly:
H2 + Br2 = 2HBr.

10.

3.Influence of the concentration of reactants on the rate
of a chemical reaction
With an increase in the concentration of reacting substances, a greater number
of collisions occur, leading to chemical interaction of particles of substances
with each other.
Example:
for reaction
A + 2B = C
the rate can be expressed as the product of the concentrations of the starting
substances:
υ = k [A] ⋅ [B] ⋅ [B] = k [A] ⋅ [B] 2, where k is the proportionality coefficient.
In this case, the concentration of each substance in the reaction rate equation is
raised to a power equal to the coefficient in front of the substance formula in the
reaction equation.

11.

Law of mass action :
the rate of a chemical reaction is directly proportional to the product of the
concentrations of the reacting substances in powers equal to the coefficients in
front of the formulas of the substances in the reaction equation.
The equation of the reaction rate according to the law of mass action for the
reaction
aA + bB = cC + dD
looks like:
υ = k [A]a⋅ [B]b.
The proportionality coefficient k is called the rate constant.
It is numerically equal to the reaction rate at a concentration of reactants of 1
mol / l.

12.

The kinetic equation of the reaction is an equation that establishes the
dependence of the reaction rate on the concentration of the reacting
substances.
The concentration of only liquid (dissolved) and gaseous substances
is written into the kinetic equation, since they participate in the
reaction throughout the volume of the mixture of substances
(solution).
Pay attention!
Concentrations of solids are not written into the kinetic equation.
Their concentration is not taken into account, because the reaction
occurs only on their surface.
However, for solids, the reaction rate depends on the degree of
grinding of the substance, that is, on the size of the surface on which
the reaction takes place.

13.

3.Effect of temperature on the rate of chemical reaction
The rate of most reactions increases with increasing temperature.
According to the Van't Hoff rule:
when the temperature rises for every 10 ° C, the rate of most reactions
increases 2 to 4 times.
v
v
t2
t1
t 2 t1
10
where gamma (ɣ) is the temperature coefficient, which shows how many
times the reaction rate will increase when the temperature rises by 10 ° C.

14.

An increase in the reaction rate with increasing temperature is
associated not only with an increase in kinetic energy and the
number of collisions of particles of reacting substances.
If all the colliding particles reacted with each other, the reaction
would be like an explosion!
But some of the collisions do not lead to the formation of new
substances (a).

15.

The reaction occurs only as a result of effective collisions
(b) of particles with excess energy - activation energy.
This energy is enough to break or weaken bonds, which
can lead to the rearrangement of atoms into new
molecules.
As the temperature rises, the proportion of active
molecules increases; the number of effective collisions
increases. Thus, the rate of the chemical reaction
increases.

16.

4.Effect of a catalyst on the rate of a chemical reaction
Catalysts are substances that speed up a chemical reaction.
In this case, the catalysts themselves are not consumed during the
reaction.
The opposite in action to catalysts is inhibitors - substances that
slow down a chemical reaction.
The phenomenon of a change in the rate of reaction in the presence
of catalysts is called catalysis.
Catalytic reactions are reactions involving catalysts.

17.

The mechanism of action of catalysts is associated with
a change in the path of the overall reaction due to the
formation of intermediate compounds with the catalyst.
Intermediates have a lower activation energy, which
significantly increases the reaction rate.

18.

Catalysis can be homogeneous or heterogeneous.
With homogeneous catalysis, the reactants and the catalyst are
in the same state of aggregation.
In heterogeneous catalysis, the reactants and the catalyst are in
different states of aggregation.
Catalysis is widely used in industry and is widespread in nature.
Enzymes, which are biological catalysts, play an important role
in living organisms. Unlike inorganic catalysts, they have a
special specificity and act under milder conditions.

19.

Questions for self control
1.Complete the sentence.
Chemical reaction rate ...
A)independent of temperature
B)depends on temperature
C)depends on the concentration of reaction products
D)does not depend on inhibitor
2. Note which of the statements is true for the law of mass action:
A)concentration of liquid substances cannot be written into the kinetic
equation
B)in the kinetic equation, the concentration of liquid substances can be
written
3. Choose the correct statements (multiple answers):
A)the dependence of the reaction rate on temperature expresses the
Van't Hoff rule
B)intermediate compounds of substances with a catalyst can increase
the reaction rate
C)when the temperature rises by one degree, the rate of most reactions
increases two to four times
D)inhibitors - substances that speed up a chemical reaction

20.

4.Choose the correct statement for homogeneous catalysis :
A)the aggregate state of the catalyst and the starting materials is different
B)the catalyst is in the same state of aggregation as the reaction products
C)the catalyst is in the same state of aggregation as the reactants
5. Determine the reaction rate
A + B = AB,
if the initial concentration of substance B was 3.9 mol / l, and after 2
seconds, the concentration of substance B became 1.8 mol / l .
6. Find how many times the reaction speed will increase
A + 2B = AB
with an increase in the concentration of the starting reagents 5 times
(s).
7. Calculate how many times the reaction rate will increase
B + C = BC,
if the initial temperature was 20 ° С, and after a while became 60 ° C.
The temperature coefficient of the reaction is 2.

21.

Literature
1.Basic literature :
1. Jenkins, Chemistry, ISBN 978-0-17-628930-0
2. Alberta Learning, Chemistry data booklet 2010, product №755115, ISBN 10645246
3.М.К.Оспанова, К.С.Аухадиева, Т.Г. Белоусова Химия: Учебник 1,2 часть для 10 класса
естественно-математического направления общеобразовательных школ Алматы: Мектеп, 2019г.
4.М.К.Оспанова, К.С.Аухадиева, Т.Г. Белоусова Химия: Учебник 1,2 часть для 11 класса
естественно-математического направления общеобразовательных школ Алматы: Мектеп, 2020 г.
5. М.Оспанова, К.Аухадиева, Т.Белоусова Химия. Дәрислик. 1, 2-қисим Алматы: Мектеп, 2019
6. М.Успанова, К.Аухадиева, Т. Белоусова
Химия. Дарслик. 1, 2 - қисм Алматы: Мектеп, 2019
7. Т.Г.Белоусова, К.С. Аухадиева Химия: Методическое руководство 1, 2 часть естественноматематического направления общеобразовательных школ Алматы: Мектеп, 2019 г.
8. Темирбулатова А., Сагимбекова Н., Алимжанова С.,Химия. Сборник задач и упражнений
Алматы: Мектеп, 2019 г.

22.

2.Additional literature :
1.Б.А.Мансуров «Химия» 10-11 кл., Атамура 2015 г
2.Б.Мансуров., Н.Торшина «Методика преподавания органической химии»
Атамура 2015г.
3.А.Е.Темирбулатова, Н.Н.Нурахметов, Р.Н.Жумадилова, С.К.Алимжанова
Химия: Учебник для 11 класса естественно-математического направления
общеобразовательной школы Алматы: Мектеп, 2015г. -344 стр.
4.Г.Джексембина «Методическое руководство» Алматы: Мектеп, 2015г
5.А.Темирболатова., А.Казымова., Ж.Сагымбекова «Книга для чтения»
Мектеп 2015г.
6. Торгаева Э., Шуленбаева Ж. и др Химия.Электронный учебник.10класс.2016 Национальный центр информатизации
7. Жакирова Н., Жандосова И. и др Химия.Электронный учебник.11класс.2016 Национальный центр информатизации
8.Эектронные ресурсы с www.bilimland.kz

23.

Do you have any questions?