How do you find the *average* rate of a reaction if the rate is NOT constant?

Answer 1

You can find the slope between two points and that will be the average between those two points. The average will change depending on which points you use.

Unless it’s a zero order reaction, the rate will never be constant.

Answer 2

Hi Marian,

It can help to think of an analogy to speed.

The average speed of a trip—which is the rate of change of distance with time—is the distance traveled divided by the total time it took for the trip. You can still find that average speed even if your speedometer (your instantaneous speed) was not constant during the trip.

The average rate of a reaction A → B is the total amount of A consumed or the amount of B produced (or the change in their concentrations) divided by the total time it took for that change to happen. You can still find that average speed even if the instantaneous rate of reaction was not constant during the time the reaction took place.