Concentration-Time Graphs
Reaction Order Using Concentration-Time Graphs
- In a zero-order reaction, the concentration of the reactant is inversely proportional to time
- This means that the reactant concentration decreases as time increases
- The graph is a straight line going down as shown:
Concentration-time graph of a zero-order reaction
- The gradient of the line is the rate of reaction
- Calculating the gradient at different points on the graph, will give a constant value for the rate of reaction
- When the order with respect to a reactant is 0, a change in the concentration of the reactant has no effect on the rate of the reaction
- Therefore:
Rate = k
- This equation means that the gradient of the graph is the rate of reaction as well as the rate constant, k
- In a first-order reaction, the concentration of the reactant decreases with time
- The graph is a curve going downwards and eventually plateaus:
Concentration-time graph of a first-order reaction
- In a second-order reaction, the concentration of the reactant decreases more steeply with time
- The concentration of reactant decreases more with increasing time compared to a first-order reaction
- The graph is a steeper curve going downwards:
Concentration-time graph of a second-order reaction