Monitoring the rate of a reaction
The rate of a chemical reaction is a measure of how fast the reactants are being used up and how fast the products are being made.
The rate can be determined by measuring:
- changes in the concentration of the reactants or products
- changes in the mass of the reactants or products
- changes in the volume of the reactants or products
For example, when dilute hydrochloric acid reacts with zinc metal, zinc chloride and hydrogen gas are produced.
There are two simple ways to measure the rate of this reaction in the lab.
1. If the reaction is set up on a balance as shown, the mass of the apparatus can be monitored throughout the reaction. As hydrogen bubbles escape, the apparatus will lose mass.
2. An alternative way to monitor the reaction is by collecting and measuring the volume of the gas as it is produced. The gas can be collected in a gas syringe or over water (as long as it is insoluble in water).
Watch this video to see how a gas syringe is used to measure the volume of gas produced when magnesium carbonate reacts with dilute hydrochloric acid.
Demonstration of how a gas syringe can be used to measure gas produced by a reaction