Rate-Concentration Graphs
Reaction order using rate-concentration graphs
- In a zero-order reaction, the rate doesn’t depend on the concentration of the reactant
- The rate of the reaction therefore remains constant throughout the reaction
- The graph is a horizontal line
- The rate equation is rate = k
Rate-concentration graph of a zero-order reaction
- In a first-order reaction, the rate is directly proportional to the concentration of a reactant
- The rate of the reaction increases as the concentration of the reactant increases
- This means that the rate of the reaction decreases as the concentration of the reactant decreases when it gets used up during the reaction
- The graph is a straight line
- The rate equation is rate = k[A]
Rate-concentration graph of a first-order reaction
- In a second-order reaction, the rate is directly proportional to the square of concentration of a reactant
- The rate of the reaction increases more as the concentration of the reactant increases
- This means that the rate of the reaction decreases more as the concentration of the reactant decreases when it gets used up during the reaction
- The graph is a curved line
- The rate equation is rate = k[A]2
Rate-concentration graphs of a second-order reaction
Exam Tip
Careful - sometimes when asked to complete calculations for the rate constant, k, the exam question will give you a graph as well as tabulated data. Do not ignore the graph as this demonstrates the order of one of the reactants, while the tabulated data allows you to determine the order for the other reactants.
