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.

Two rectangular diagrams comparing particle concentration. Diagram 1, labelled "LOWER concentration", displays fewer green and red particles. Diagram 2, labelled "HIGHER concentration", has a denser distribution of the same green and red particles.

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.

Two rectangular diagrams comparing particle pressure. Diagram 1, labelled "LOWER Pressure", shows green and red particles spaced apart (in a larger container). Diagram 2, labelled "HIGHER Pressure", presents the same green and red particles in closer proximity to each other (in a smaller container).

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.

A graph depicting the relationship between the total mass or volume of a product and the time from the start of a reaction. The x-axis represents the "Time from start of reaction", and the y-axis denotes "Total mass/volume of product". Two curves are shown: a red curve for "High concentration or high pressure", which rises steeply and levels off higher on the y-axis, and a blue curve for "Low concentration or low pressure", which rises more gently and levels off lower on the y-axis.

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