Reactions occur when particles of reactants collide with a certain minimum kinetic energy:
- at higher concentratiosn and higher pressures, the particles are in closer proximity to each other encouraging more frequent collisions
- at higher temperature, a much higher proportion of colliding particles have sufficient energy to react and more particles are able to overcome the activation enthalpy barrier
- with smaller particles of reactant there is a larger surface area on which the reactions can take place, so the greater the chance of successful collisions
- heterogeneous catalysts provide a surface where reacting particles may break and make bonds
All of the above serve to increase the rate of a chemical reaction.
The activation enthalpy is the minimum kinetic energy required by a pair of colliding atoms or molecules before a reaction will occur.
An enthalpy profile shows hwo the enthalpy changes as a reaction proceeds.