3.5 Chemical Kinetics
Year 12 Recap
Measuring Rates of Reaction
We can either measure the formation of the products or the decrease in reactants
- Gas Collection
- Measuring pH change
- Decrease in mass
- Colorimetry
Gas Collection
Measure the change in volume of gas at set time
intervals
Rate = change in volume/time
Example
Na2CO3 (s) + 2HCl (aq) 2NaCl (aq) + CO2 (g) + H2O (l)
Gas collection would be a suitable method as a gas
is given off and you are able to measure the change
in volume of gas over set time intervals
Measuring Decrease in Mass
Measure the change in mass at set time intervals
Rate = change in mass/time
- Use cotton wool to stop acid spray escaping
- Could improve the precision of scales for
more accuracy
Example
Na2CO3 (s) + 2HCl (aq) 2NaCl (aq) + CO2 (g) + H2O (l)
Measuring decrease in mass would be a suitable method as a gas is given off so you are able to
measure the decrease in mass at set time intervals
, Colorimetry
Measures the formation of coloured product or the disappearance of coloured reactants
1. Calibrate the colorimeter with a solution of known concentration of the coloured species
2. Pass a light of a specific frequency through a sample of the reaction mixture at set time
intervals
3. The amount of light that passes through the sample is detected and will be different for
differing concentrations of the coloured species
This allows us to determine the change in concentration over time which is the rate of reaction
Example
S2O82- (aq) + 2I- (aq) 2SO42- (aq) + I2 (aq)
Colorimetry would be a suitable method as there is a colour change with the production of red-
brown Iodine
1. Start by callibrating the colorimeter against a known concentration of I2.
2. Pass light of a specific frequency through the reaction mixture at set time intervals.
3. The amount of light passing through will be detected as the concentration of I2 increases
which means we are able to measure the rate of reaction.
Factors Effecting the Rate of a Chemical Reaction
Collision theory – in order to react, particles have to collide with enough energy. Any change made
to conditions that can increase the number of collisions and/or energy the particle possess will
increase the rate of reaction.
Activation Energy – The minimum amount of energy required to start a reaction.
Year 12 Recap
Measuring Rates of Reaction
We can either measure the formation of the products or the decrease in reactants
- Gas Collection
- Measuring pH change
- Decrease in mass
- Colorimetry
Gas Collection
Measure the change in volume of gas at set time
intervals
Rate = change in volume/time
Example
Na2CO3 (s) + 2HCl (aq) 2NaCl (aq) + CO2 (g) + H2O (l)
Gas collection would be a suitable method as a gas
is given off and you are able to measure the change
in volume of gas over set time intervals
Measuring Decrease in Mass
Measure the change in mass at set time intervals
Rate = change in mass/time
- Use cotton wool to stop acid spray escaping
- Could improve the precision of scales for
more accuracy
Example
Na2CO3 (s) + 2HCl (aq) 2NaCl (aq) + CO2 (g) + H2O (l)
Measuring decrease in mass would be a suitable method as a gas is given off so you are able to
measure the decrease in mass at set time intervals
, Colorimetry
Measures the formation of coloured product or the disappearance of coloured reactants
1. Calibrate the colorimeter with a solution of known concentration of the coloured species
2. Pass a light of a specific frequency through a sample of the reaction mixture at set time
intervals
3. The amount of light that passes through the sample is detected and will be different for
differing concentrations of the coloured species
This allows us to determine the change in concentration over time which is the rate of reaction
Example
S2O82- (aq) + 2I- (aq) 2SO42- (aq) + I2 (aq)
Colorimetry would be a suitable method as there is a colour change with the production of red-
brown Iodine
1. Start by callibrating the colorimeter against a known concentration of I2.
2. Pass light of a specific frequency through the reaction mixture at set time intervals.
3. The amount of light passing through will be detected as the concentration of I2 increases
which means we are able to measure the rate of reaction.
Factors Effecting the Rate of a Chemical Reaction
Collision theory – in order to react, particles have to collide with enough energy. Any change made
to conditions that can increase the number of collisions and/or energy the particle possess will
increase the rate of reaction.
Activation Energy – The minimum amount of energy required to start a reaction.
