Summary AQA GCSE Chemistry Combined Science - Rate and Extent of Chemical Change Notes

THE RATE AND EXTENT OF CHEMICAL
CHANGE

COLLISION THEORY AND ACTIVATION ENERGY
 Activation energy: minimum amount of energy that particles require to react
 Collision theory: chemical reactions can occur only when reaction particles collide with each
other and with sufficient energy
 Increasing concentration of reactants, pressure of reacting gases and surface area of solid
reactants increases the frequency of collisions and so increases the rate of reaction
 Increasing the temperature increases the frequency of collisions and makes them more
energetic, and so increases the rate of reaction




EQUILIBRIUM
 Equilibrium: when both the forward and reverse reactions occur at the same rate in a closed
system
 EFFECT OF CHANGING CONCENTRATION
o If concentration of reactants is increased: the position of equilibrium shifts towards
products so more product is produced
o If concentration of products is increased: the position of equilibrium shifts towards
reactants so more reactant is produced
 EFFECT OF CHANGING TEMPERATURE
o If temperature is increased: equilibrium moves in the direction of the endothermic
reaction
 Exothermic: decreases yield of reaction
 Endothermic: increases yield of reaction
o If temperature is decreased: equilibrium moves in the direction of the exothermic
reaction
 Exothermic: increases yield of reaction
 Endothermic: decreases yield of reaction
 EFFECT OF CHANGING PRESSURE
o If pressure is increased
 Larger volume of gas (more moles): decreases yield of reaction
 Smaller volume: increases yield of reaction
o If pressure is decreased:
 Larger volume: increases yield of reaction
 Smaller volume: decreases yield of reaction