Rates of reaction

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.