Chemical Kinetics
4.0 Order of a reaction
4.0 Order of a reaction
Order of a reaction is always found by doing experiments. Let us assume a chemical reaction $$aA + bB \to cC\quad ...(1)$$
As we have studied about the rate of reaction. So, using experiments we can find out the rate of a reaction by changing the concentration of reactants. For example, if the rate law is defined as $$R = k\left[ A \right]$$ We can say that if we double the concentration of $A$ then the rate of reaction will also get doubled.
In similar way, if the rate law is defined as $$R = k{\left[ A \right]^2}$$ We can say that if we double the concentration of $A$ then the rate of reaction will be ${2^2} = 4$ times the previous rate.
Using this experimental technique, we can generalized the results for equation $(1)$ i.e., $$Rate = k{\left[ A \right]^a}{\left[ B \right]^b}$$ where $k$ is the rate constant, $a$ is the order of reaction with respect to $A$ and $b$ is the order of reaction with respect to $B$.
Note:
- Value of order can be $0$ or any whole number as well as in fraction i.e, $2.5$.
- Overall order of a reaction is found by adding all the coefficients of rate law equation. In equation $(1)$ it is $(a+b)$.
