## Graphs and Le Chatelier’s principle

Graphs can be used to represent data about equilibrium reactions. The following are some points to keep in mind when presented with a graph.

Identify the type of graph by looking at the label on the y-axis. You will find either:

a rate-time graph

a mole-time or concentration-time graph

For rate-time graphs, when the rate for the forward reaction and the rate for the reverse reaction are equal, the system is in equilibrium.

For concentration-time graphs or mole-time graphs equilibrium occurs where the concentration or number of moles of the reactants and products are

**constant**. These values need not be equal to one another.When calculating \(\text{K}_{\text{c}}\) make sure you only take values from the sections of the graph where the y-value is constant. \(\text{K}_{\text{c}}\) can only be calculated when the system is in equilibrium.