Topic 9: Kinetics I
1. understand, in terms of collision theory, the effect of a change in
concentration, temperature, pressure and surface area on the rate of a
chemical reaction
Factors affecting rate of reaction:
Temperature:
Increasing the temperature means the particles on
average will have more kinetic energy and move faster.
A greater proportion of molecules will therefore have
activation energy and be able to react. The molecules
are moving faster so will collide more often and with a
greater force, increasing rate of reaction.
Pressure:
Increasing the pressure of a gas means there are more
particles in a given volume, so there will be more
collisions, increasing the frequency of successful
collisions.
Concentration:
Increasing the concentration in a solution means there
are more reacting particles in a given volume, so the
particles will collide more frequently, increasing the
chance of a successful collision.
Surface Area:
Increasing surface area means there are more particles
exposed and available to react, so there will be more
collisions between reactant particles, increasing the
chance of successful collisions.
2. understand that reactions only take place when collisions take place with
sufficient energy, known as activation energy
Collision Theory:
A reaction between two particles won’t take place unless:
The particles are facing in the right direction
They collide with the minimum amount of kinetic
energy (activation energy)
Activation energy: the minimum quantity of energy which the reacting species must possess in
order to undergo a specified reaction
Particles need activation energy to break the bonds to start the reaction. Reactions with low
activation energy will happen quite easily. Reactions with high activation energies may need to
be given extra energy by heating them so the particles have activation energy.
EA on a reaction profile diagram:
1. understand, in terms of collision theory, the effect of a change in
concentration, temperature, pressure and surface area on the rate of a
chemical reaction
Factors affecting rate of reaction:
Temperature:
Increasing the temperature means the particles on
average will have more kinetic energy and move faster.
A greater proportion of molecules will therefore have
activation energy and be able to react. The molecules
are moving faster so will collide more often and with a
greater force, increasing rate of reaction.
Pressure:
Increasing the pressure of a gas means there are more
particles in a given volume, so there will be more
collisions, increasing the frequency of successful
collisions.
Concentration:
Increasing the concentration in a solution means there
are more reacting particles in a given volume, so the
particles will collide more frequently, increasing the
chance of a successful collision.
Surface Area:
Increasing surface area means there are more particles
exposed and available to react, so there will be more
collisions between reactant particles, increasing the
chance of successful collisions.
2. understand that reactions only take place when collisions take place with
sufficient energy, known as activation energy
Collision Theory:
A reaction between two particles won’t take place unless:
The particles are facing in the right direction
They collide with the minimum amount of kinetic
energy (activation energy)
Activation energy: the minimum quantity of energy which the reacting species must possess in
order to undergo a specified reaction
Particles need activation energy to break the bonds to start the reaction. Reactions with low
activation energy will happen quite easily. Reactions with high activation energies may need to
be given extra energy by heating them so the particles have activation energy.
EA on a reaction profile diagram:
