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# How do you calculate the average rate of the reaction?

Last updated date: 11th Aug 2024
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Hint: The average rate of reaction is calculated by dividing the change in concentration of the reactant or the change in concentration of the product over a specific time duration by the time interval.

The average rate of the reaction is defined as the ratio of the change in the concentration of the reactant taking part in the chemical reaction or the change in the concentration of the product formed in the chemical reaction to the time interval.
Consider a reaction shown below.
$aA + bB \to cC + dD$
In calculating the average rate of reaction over the time interval, the change in concentration over the given time interval is divided by the time interval.
When we deal with the reactant, the average rate of reaction is given as shown below.
$The\;rate\;of\;reaction\;of\;A = - \dfrac{{\Delta [A]}}{{\Delta t}}$
The minus sign is used to make the rate a positive number.
When we deal with the product, the average rate of reaction is given as shown below.
$The\;rate\;of\;reaction\;of\;C = \dfrac{{\Delta [C]}}{{\Delta t}}$
For product minus sign is not used.
The overall rate of the reaction will be the same whichever component we measure.
Divide the rate of each component with the coefficient, so the rate of reaction is given as shown below.
$The\;rate\;of\;reaction\; = - \dfrac{1}{a}\dfrac{{\Delta [A]}}{{\Delta t}} = - \dfrac{1}{b}\dfrac{{\Delta [B]}}{{\Delta t}} = \dfrac{1}{c}\dfrac{{\Delta [C]}}{{\Delta t}} = \dfrac{1}{d}\dfrac{{\Delta [D]}}{{\Delta t}}$

Note:
The average rate of the reaction can either be positive in value or negative in value. The average rate of the reaction is positive when the rate of the concentration of the product formed in the reaction increases. The average rate of reaction is negative when the rate of the concentration of the reactant taking part in chemical reaction decreases.