How do you calculate rate from a concentration-time graph?

You calculate rate from a concentration-time graph by determining the gradient of the line at any given point.

In more detail, the rate of a reaction can be calculated from a concentration-time graph by determining the gradient (slope) of the line. The gradient of the line on a concentration-time graph represents the rate of reaction. The steeper the gradient, the faster the rate of reaction.

To calculate the rate at a specific point in time, you need to draw a tangent to the curve at that point and then calculate the gradient of this tangent. The gradient of a line is calculated by dividing the change in the y-axis (concentration) by the change in the x-axis (time). In other words, it's the change in concentration per unit of time.

For example, if the concentration of a reactant decreases from 0.5 mol/dm³ to 0.3 mol/dm³ in 2 seconds, the rate of reaction would be (0.5-0.3) mol/dm³ / 2 s = 0.1 mol/dm³/s. This means that the concentration of the reactant is decreasing by 0.1 mol/dm³ every second, indicating the speed of the reaction.

If the graph is a straight line, the reaction rate is constant and the gradient can be calculated between any two points on the line. However, if the graph is a curve, the reaction rate is changing over time. In this case, you need to draw tangents at different points on the curve to calculate the rate at those specific times.

Remember, a negative gradient indicates a decrease in concentration over time (as in the case of reactants), while a positive gradient indicates an increase in concentration over time (as in the case of products).

In summary, the rate of a reaction from a concentration-time graph can be calculated by determining the gradient of the line or tangent at a given point, representing the change in concentration over time.