Rate Graphs

When you plot the mass or volume of product formed against time for a chemical reaction, you will usually get a curved graph. This curve represents how the rate of reaction changes over time. You can see this in the diagram below for two different reactions:

A Reaction graph with the y-axis labelled "Total mass/volume of product" and the x-axis labelled "Time from start of reaction". 2 lines go upwards and then plateau meeting each other with a red line on the top line reading "fast reaction" and a blue line on the bottom line reading "slow reaction".

The rate of reaction constantly changes, so you need to pick a specific point. To calculate the rate at a specific point, you need to draw a tangent to the curve and measure its slope.

The steeper the gradient of the tangent, the greater the rate of reaction. When the gradient of the tangent becomes zero, the reaction is complete and no further product is formed.

  • When the tangent is a horizontal line, its gradient is zero.

You’ve used 0 of your 10 free revision notes for the month

Sign up to get unlimited access to revision notes, quizzes, audio lessons and more

Sign up