Monthly Archives: January 2019

Language of rates of reaction

This applies to both A-level and GCSE. It is amazing how many marks are thrown away when writing about the collision theory.

Increasing temperature, concentration and surface area all increase the frequency of collisions. 

It is not enough to say only there are more collisions as there is no reference to time.

More collisions per second is fine though.

A greater chance of collisions is not good enough as probability is not the same as frequency (This is sometimes accepted though.)


When talking about increased concentration then say there are more particles per unit volume.  

More particles on its own is not good enough.


When talking about temperature the particles have more energy and move faster. They therefore collide more frequently. More particles will also collide with more energy than the activation energy. Leading to more successful collisions.

Be careful with activation energy. Sometimes candidates write particles have more activation energy. This is not correct though.

Activation energy  is the minimum energy needed for the collision to be successful. Particles can’t have more or less activation energy.  Particles can only have more or less energy than the activation energy. ( just two missing words completely changes the meaning)

If the particles have less energy than the activation energy they bounce off each other and do not react. If the particles have more energy than the activation energy then they react.