We usually use water displacement method to collect gas in school laboratory as shown below:
- The reaction is fastest at the start when the reactants are at a maximum (steepest gradient)
- The gradient becomes progressively less as reactants are used up and the reaction slows down.
- Finally the graph levels out when one of the reactants is used up and the reaction stops.
- The amount of product depends on the amount of reactants used.
- The initial rate of reaction is obtained by measuring the gradient at the start of the reaction. A tangent line is drawn to measure rate of reaction at instataneous time.