activation energy

what is activation energy?

the minimum energy that colliding particles must posses for a reaction to occur

when can k change?

k only remains constant if the concentration of the reactants is the only factor which is changed

• If the temperature is changed or a catalyst is used or changed, then the rate constant, k, changes

effect of temperature on the rate constant

• an increase in temperature increases the number of particles with E> Ea so frequency of successful collisions increases

• a small increase in temperature has a greater impact on the rate

• Since the rate constant and rate of reaction are directly proportional to the fraction of molecules with energy equal or greater than the activation energy, then at higher temperatures:

  • The rate of reaction increases

  • The rate constant increases

what is catalyst 

a substance that increases the rate of reaction but is chemically unchanged at the end. It provides an alternative pathway with lower activation energy

what is homogenous catalyst

• in the same state/phase as the reactants

what is heterogenous catalyst

catalyst in a different phase to the reactant

how heterogenous catalyst works

1) Adsorption: the reactants are adsorbed onto surface of the catalyst

2) Reaction: the reactants form temporary bonds with teh catalyst, weakening their bonds within the mlecule. A porduct is formed

3) Desorption: the products leave the surface of the catalyst