Calculating rate of reaction

Average rate of reaction

The rate of reaction can change during the course of a reaction. The average rate of reaction can be calculated using:

  • data from a table of results, or
  • values from a graph
Rate of reaction graphTo find the average rate of reaction at 20 seconds, read off the volume of product for this time

To find out the average rate of reaction at 20 seconds:

\frac{volume~of~product}{time} = \frac{40}{20}

= 2 cm3/s

Question

During a reaction between hydrochloric acid and calcium carbonate, it takes 20 seconds to collect 80 cm3 of carbon dioxide.

What is the average rate of reaction over this time?

The average rate of reaction

\frac{volume~of~product}{time}

\frac{80}{20}

= 4 cm3/s

Rate of reaction at a specific time

The rate of reaction at a specific time is equal to the gradient of the graph at that time - it is equal to the gradient of the tangent.

Rate of reaction graph tangent

Rate of reaction at 20 seconds

= gradient of tangent

= \frac{60}{20}

= 3 cm3/s