Effect of Concentration & Pressure (Oxford AQA International A Level Chemistry)
Revision Note
Written by: Philippa Platt
Reviewed by: Stewart Hird
Concentration & Rate of Reaction
The more concentrated a solution is, the greater the number of particles in a given volume of solvent
An increase in concentration causes in an increased collision frequency and therefore an increased rate of reaction
As the reactants are used up their concentration falls
Therefore, the reaction rate decreases over time
The diagram shows a higher concentration of particles in (b) which means that there are more particles present in the same volume than (a) so the chances and frequency of collisions between reacting particles is increased causing an increased rate of reaction
Pressure & Rate of Reaction
An increase in pressure in reactions that involve gases has the same effect as an increase in the concentrations of solutions
When the pressure is increased, the molecules have less space in which they can move
This means that the number of effective collisions increases due to an increased collision frequency
An increase in pressure, therefore, increases the rate of reaction
The diagram shows a higher pressure in (b) which means that the same number of particles occupy a smaller volume, resulting in an increased collision frequency and therefore increased rate of reaction
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