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