Chapter 1: Rate of Reaction

1. CHAPTER 1
Rate of Reaction

2. Learning Outcomes
You should be able to :
state what rate of reaction is,
identify observable changes to reactants or products
for determining rate of reaction,
determine the average rate of reaction,
determine the rate of reaction at any given time from
a graph,
solve numerical problems involving average rate of
reaction.
solve numerical problems involving rate of reaction
at any given time.

3. What is rate of reaction?
Rate of reaction:
The speed at which reactants are converted into
products in a chemical reaction
As the reaction proceeds:
The amount of reactants decreases
The amount of products increase

4. Classification:
• Fast reaction : the time taken is short
the rate of reaction is high
• Slow reaction : the time taken is long
the rate of reaction is low

5. Measuring the rate of reaction
Observable changes ( visible changes )
Suitable changes which can be observed in a
chemical reaction:
a) volume of gas liberated
b) time taken for the precipitate formed
c) change in mass during the reaction
d) colour changes
e) temperature changes
f) pressure changes

6. Rate of reaction = change in selected quantity
time taken
Example :
Rate of reaction = decrease in mass of CaCO3
time taken
OR
Rate of reaction = increase in volume of CO2
time taken

7. Measurement rate of reaction
1. Average rate of reaction :
Average value of the rate of reaction within a
specified period of time.
a) Average rate of reaction in the first 3 minutes,
b) Average rate of reaction in the third minute
c) Overall average rate of reaction

8. 2. Rate of reaction at a given time:
The actual rate of reaction at that instant.
Also known as :
The instantaneous rate of reaction
Rate of reaction = Gradient of the
at a given time curve at that instant

9. Step 1
Draw a tangen (line DE) on the
curve at time t.
Step 2
Draw the right-angled triangle
DEF.
Step 3
Measure the length of DF and EF.
Step 4
Calculate the gradient of the
tangent DE.
Total volume of gas (cm3)
Time (s)
t
D
E F
Rate of reaction at time t,
= gradient of curve at time t
= length of DF
length of EF
cm3 s-1