## Using graphs: linear relationships

Many of the relationships between two variables in chemistry can be expressed in linear form, thus producing a linear graph when experimental data is plotted. Often the value of the gradient of a line can be related to a physical constant, that we wish to measure. Therefore it is important for students to understand the equation of a straight line and how to use it.

**y = mx + c**

where **m** is the gradient or slope of the graph and **c** is the intercept, where the line crosses the y-axis.

The gradient m is calculated from the expression

For students to be able to understand the equation of a straight line and then relate it to the chemical phenomena they must have a basic understanding of algebra.

The equation of a straight line is used in the following examples, which were taken from Paul Yates' article Using the equation of a straight line. The article is a useful source of further reading as it provides useful teaching tips for introducing the graphs to students and further food for thought.

**Example 1 **
The Beer Lambert law

**Example 2 **
First Order Kinetics