You can determine the reaction rate from a concentration-time graph by calculating the gradient of the line at any specific point.

To elaborate, the rate of a reaction is represented by the gradient (or slope) of the line on a concentration-time graph. A steeper gradient indicates a faster reaction rate.

To find the rate at a particular moment, you need to draw a tangent to the curve at that point and calculate the gradient of this tangent line. The gradient is determined by the formula:

where $\Delta y$ represents the change in concentration (y-axis) and $\Delta x$ represents the change in time (x-axis). Essentially, this measures the change in concentration per unit of time.

For instance, if the concentration of a reactant decreases from $0.5 \, \text{mol/dm}^3$ to $0.3 \, \text{mol/dm}^3$ over a span of $2$ seconds, the rate of reaction can be calculated as follows:

This result indicates that the concentration of the reactant is decreasing at a rate of $0.1 \, \text{mol/dm}^3$ every second, reflecting the speed of the reaction.

If the graph is a straight line, the reaction rate remains constant, and you can compute the gradient between any two points on that line. Conversely, if the graph is curved, the reaction rate changes over time. In such cases, you need to draw tangents at various points on the curve to calculate the rate at those specific moments.

It is important to note that a negative gradient signifies a decrease in concentration over time (typical for reactants), while a positive gradient indicates an increase in concentration over time (as seen with products).

In summary, the rate of a reaction can be determined from a concentration-time graph by calculating the gradient of the line or the tangent at a given point, which reflects the change in concentration over time.