Rate of Reaction.pdf

1 of 39 © Boardworks Ltd 2007

© Boardworks Ltd 2007
2 of 39
Content
1. Meaning and Measurement of Rate of
Reactions
2. Rate Expression and Rate Constant
3. Factors Affecting Rate
4. Collision Theory

3 of 39
●

4 of 39
●

5 of 39
Exercise 1
1. Assume that we have a solution of H2SO4 0.5 M in the laboratory. What
volume of H2SO4 0.5 M solution is required to obtain 0.005 mol of H2SO4?
2. Find out the molarity of the following solutions:
a) 7.1 g of sodium sulfate (Na2SO4) in 250 mL solution. (Ar Na=23, S=32,
O=16)
b) 0.002 mol of Fe(NO3)2 in 15 mL solution.
3. A student plans to make a 250 mL solution of 0.1 M K2SO4. How many
grams of K2SO4 must be used? (Ar K=39, S=32, O=16)
4. What is the volume of a 0.5 M H2SO4 solution needed to prepare a solution
of 0.2 M H2SO4 using a 250 mL volumetric flask?
5. Hydrochloric acid (HCl) contain 37% of HCl mass and density of 1.19 kg/L
a) Determine the molarity of the solution! (Ar H=1, Cl=35.5)
b) What is the volume of solution needed to prepare about 500 mL of HCl
4M?

6 of 39
MEANING AND
MEASUREMENT OF RATE OF
REACTIONS

7 of 39
Meaning & Measurement of Rate of Reactions
The rate of the reaction is the change of concentration
a substance divided by the time interval.
for example :
A + B → C + D
time
ion
concentrat
)
(
reaction
of
Rate





8 of 39
• When the reaction takes places, the amount of reactant
A & B decreases and the amount of product C & D
increases.
t
[D]
D
D
of
reaction
of
Rate
t
[C]
C
C
of
reaction
of
Rate
t
[B]
-
B
B
of
reaction
of
Rate
t
[A]
-
A
A
of
reaction
of
Rate























9 of 39
• For reaction with different coefficient.
mA + nB → oC + pD
The relation
D
p
C
o
B
n
A
m




1
1
1
1








10 of 39
Example
The formation of ammonia is given by the following reaction
N2(g) + 3H2(g) → 2NH3(g)
If in certain time t, the rate of formation of NH3 is 0,5 M/s, determine
a) the rate of reaction for N2
b) the rate of reaction for H2
Answer
N2(g) + 3H2(g) → 2NH3(g)
0,5 M/s
a) the rate of reaction for N2 b) the rate of reaction for H2
25
,
0
5
,
0
2
1
2
1
3
2




 NH
N 

0,75
5
,
0
2
3
2
3
3
2




 NH
H 


11 of 39
Example
0.05 mol of SO3 gas is produced in 1 L container within 2 minutes
according to the reaction below. Find the rate of consumption of SO2
and O2 gases in M/s.
2SO2(g) + O2(g) → 2SO3(g)

12 of 39
Example
• Find the rate relationship of reactants and products for the given
reaction.
N2(g) + 3H2(g) → 2NH3(g)

13 of 39
RATE EXPRESSION AND
RATE CONSTANT

14 of 39
Rate Expression and Rate Constant
• For reaction
A + B → product
The rate law is stated in the form of the rate equation as
follows :
V = k [A]x [B]y
Where,
V = rate of reaction (M/s)
k = rate of reaction constant
[A] = concentration of A
[B] = concentration of B
x = order of reaction in A
y = order of reaction in B
x + y = total order

15 of 39
Example
• Write the possible rate expression of the following reactions.
a.Cl2(g) + H2(g) → 2HCl(g)
b.Fe(s) + Cl2(g) → FeCl3(g)
c.Fe2O3(s) + 3H2SO4(aq) → Fe2(SO4)3(s) + 3H2O(l)
d.Ca(s) + 2Ag+
(aq) → 2Ca+2
(aq) + Ag(s)

16 of 39
Order of Reaction

17 of 39
What does rate of reaction mean?
The speed of different chemical reactions varies hugely.
Some reactions are very fast and others are very slow.
What is the rate of these reactions?
The speed of a reaction is called the rate of the reaction.
rusting baking explosion
slow fast very fast

18 of 39
Rates of reaction
Why are some reactions faster than others?

19 of 39
Reactions, particles and collisions
Reactions take place when particles collide with a
certain amount of energy.
The minimum amount of energy needed for the particles
to react is called the activation energy, and is different
for each reaction.
The rate of a reaction depends on two things:
l the frequency of collisions between particles
l the energy with which particles collide.
If particles collide with less energy than the activation
energy, they will not react. The particles will just bounce
off each other.

20 of 39
Changing the rate of reactions
l increased temperature
l increased concentration of
dissolved reactants, and increased
pressure of gaseous reactants
l increased surface area of solid
reactants
l use of a catalyst.
Anything that increases the number of successful collisions
between reactant particles will speed up a reaction.
What factors affect the rate of reactions?

21 of 39
Slower and slower!
Reactions do not proceed at a steady rate. They start off at a
certain speed, then get slower and slower until they stop.
As the reaction progresses, the concentration of reactants
decreases.
This reduces the frequency of collisions between particles
and so the reaction slows down.
percentage completion of reaction
100%
0% 25% 50% 75%
reactants
product

22 of 39

23 of 39
Temperature and collisions
How does temperature affect the rate of particle collision?

24 of 39
Effect of temperature on rate
The higher the temperature, the faster the rate of a reaction.
In many reactions, a rise in temperature of 10°C causes the
rate of reaction to approximately double.
Why does increased temperature
increase the rate of reaction?
At a higher temperature, particles
have more energy. This means
they move faster and are more
likely to collide with other particles.
When the particles collide, they
do so with more energy, and so
the number of successful
collisions increases.

25 of 39
Temperature and particle collisions

26 of 39

27 of 39
Effect of concentration on rate of reaction
The higher the concentration of a dissolved reactant, the
faster the rate of a reaction.
Why does increased concentration increase the rate of
reaction?
At a higher concentration, there are more particles in the
same amount of space. This means that the particles are
more likely to collide and therefore more likely to react.
higher concentration
lower concentration

28 of 39
Concentration and particle collisions

29 of 39
Effect of pressure on rate of reaction
The gas particles become closer together, increasing the
frequency of collisions. This means that the particles are more
likely to react.
Why does increasing the pressure of gaseous reactants
increase the rate of reaction?
As the pressure increases, the space in which the gas
particles are moving becomes smaller.
lower pressure higher pressure

30 of 39

31 of 39
Effect of surface area on rate of reaction
Any reaction involving a solid can only take place at the
surface of the solid.
If the solid is split into several pieces, the surface area
increases. What effect will this have on rate of reaction?
The smaller the pieces, the larger the surface area. This
means more collisions and a greater chance of reaction.
This means that there is an increased area for the reactant
particles to collide with.
low surface area high surface area

32 of 39
Surface area and particle collisions

33 of 39
reaction (time)
energy
(kJ)
What are catalysts?
Catalysts are substances that change the rate of a reaction
without being used up in the reaction.
Catalysts never produce more product – they just
produce the same amount more quickly.
Different catalysts work in
different ways, but most
lower the reaction’s
activation energy (Ea).
Ea with
catalyst
Ea without
catalyst

34 of 39
Everyday catalysts
l Nickel is a catalyst in the production of margarine
(hydrogenation of vegetable oils).
Many catalysts are transition metals or their compounds.
For example:
l Platinum is a catalyst in the
catalytic converters of car
exhausts. It catalyzes the
conversion of carbon
monoxide and nitrogen
oxide into the less polluting
carbon dioxide and nitrogen.
l Iron is a catalyst in the production of ammonia
from nitrogen and hydrogen (the Haber process).

35 of 39
Catalysts in industry
Catalysts are also essential for living cells. Biological
catalysts are special types of protein called enzymes.
Why are catalysts so important for industry?
l Products can be made more
quickly, saving time and money.
l Catalysts reduce the need for
high temperatures, saving fuel
and reducing pollution.

Rate of Reaction.pdf

More Related Content

Similar to Rate of Reaction.pdf

Recently uploaded

Rate of Reaction.pdf