Effect of Concentration on the Rate of Reaction

The two containers below show particles that can react with each other. These particles are dissolved in water, but the water particles are not shown.

One box with less green and red balls and thus only one depicted collision labelled "lower concentration" and another box with more green and red balls and thus 2 collisions labelled "higher concentration".

Both containers have the same volume, but the second container has a higher concentration of particles than the first one. This means that the particles in the second container are more crowded, which leads to more frequent collisions and a higher rate of reaction.

In reactions that involve gases, increasing the pressure will also make the particles more crowded. This is because increasing pressure causes the gas particles to be closer together. As a result, the particles collide more frequently, which increases the rate of reaction.

One box labelled "lower pressure" with a large amount of space and 4 red and 4 green balls with one collision. Then there is another smaller box labelled "higher pressure" with the same amount of balls and more collisions (2).

Rate of Reaction Graph

We can represent the effect of concentration or pressure on reaction rate using a rate of reaction graph.

The reactant at a higher concentration (solution) or higher pressure (gas) shows a higher rate of reaction than the reactant at a lower concentration or lower pressure. We know this because the line for the reaction at a higher concentration or higher pressure has a steeper gradient and it becomes horizontal faster.

Rates of reaction graph with the y-axis labelled 'total mass/volume of product' and the x-axis labelled 'time from start of reaction'. Two lines ascend then plateau, with labels pointing to each line indicating 'larger surface area' and 'smaller surface area'.