Question

Average rate of reaction definition.

Answer 1

Reaction rate can be understood as the speed at which a chemical reaction proceeds. It is often expressed in terms of either the concentration of reactant consumed in a unit of time or the product formed in a unit of time.

Complete answer:
The average rate of reaction is defined as the ratio of a measured change in amount or concentration of reactants or products of a chemical reaction in a given time interval in which the change occurred. Mathematically, it is represented as:
Average rate of reaction $= \dfrac{{\Delta X}}{{\Delta t}}$
Here, $\Delta X$ represents the change in concentration of reactants or products and $\Delta t$ represents the time interval.
Average rate of reaction is important for a reaction as sometimes the initial rate of a reaction might be different for the instantaneous rate of that reaction. The rate of a reaction can be graphically calculated by finding the slope of the concentration curve.
The average rate of reaction can be either positive or negative. Average rate of reaction is said to be positive when the rate of appearance of products increases. On the other hand, the rate of reaction is said to be negative when the rate of disappearance of reactants decreases.

Note:
Initial rate is defined as the rate of reaction at the start of the reaction (when $t = 0$). The initial rate is equal to the negative of the slope of the curve of reactant concentration versus time at $t = 0$. At any specific time, the rate at which a reaction is proceeding is known as its instantaneous rate. Hence, the initial rate of reaction can also be defined as the instantaneous rate at $t = 0$.