6.2.1 Reaction Theories

Rate of Reaction Change of concentration per unit time [department of education definition]

Collision Theory 1. Particles must collide 2. Collision only results in formation of products if a certain Minimum Energy is exceeded in the collision. Minimum Energy is called Activation Energy Called an Effective Collision

Maxwell-Boltzmann Distribution People walking on street Some very quickly Some very slowly Most moderately fast - near the average Particles in a gas at 15oC have a roughly similar distribution Draw a graph

Graph at 15oC Particles in shaded area have Activation Energy

Graph at 25oC and 15oC

Activation Energy Minimum energy two colliding particles must have in order to react [or to have an Effective Collision] Higher the temperature the more energy each particle has Thus the greater the proportion of particles that have activation energy

Size of Activation Energy depends on nature of the reactants Some have large Activation Energies so are slow or do not happen at all, because only a small fraction of the particles have sufficient energy to react Some have low Activation Energies and so react quickly

Reaction Profile Diagrams #1 Exothermic reaction ∆H

Reaction Profile Diagrams #2

Effect of catalyst on activation energy

Ea ∆H