The rate of a process is the change in the dependent variable per unit time.When a graph of a quantity against time is a straight line, the rate is constant and equals the gradient of the line.gradient = change in y ÷ change in x
Choose two points far apart on the line, find the change in y and the change in x between them, and divide.Example: the table shows the volume of oxygen produced by an aquatic plant.
Rate = (12 − 0) ÷ (8 − 0) = 1.5 cm3 min-1.The units of a rate are the units of y divided by the units of x, for example cm3 min-1.A steeper line shows a faster rate. A horizontal line shows that the rate is zero.
Choose two points far apart on the line, find the change in y and the change in x between them, and divide.Example: the table shows the volume of oxygen produced by an aquatic plant.
| Time / min | 0 | 2 | 4 | 6 | 8 |
| Volume of oxygen / cm3 | 0 | 3 | 6 | 9 | 12 |
Rate = (12 − 0) ÷ (8 − 0) = 1.5 cm3 min-1.The units of a rate are the units of y divided by the units of x, for example cm3 min-1.A steeper line shows a faster rate. A horizontal line shows that the rate is zero.