Kinetics – The Big Idea by Mr Khemistry


Kinetics is the study of speed/rate of a chemical reaction.

Definition: Rate of reaction is the change in concentration of reactant or products over time.

Question: How do we know what’s the change in concentration of reactant or products?

Ans: We have to MONITOR it.

Question: How do we monitor it?

Ans: Look at the reaction equation, what has changed from left-hand side (LHS) to the right-hand side (RHS)? We can monitor colour intensity (colourimeter), volume of gas evolved (downward displacement of water/gas syringe), loss of mass (mass balance), change in pressure (manometer), electrical conductivity, pH (pH probe, titration) etc.

Image result for colorimeter


Main Product


An important term in this chapter is “Order of Reaction”. We can only determine the order of reaction with respect to a particular reactant through experiments. Note: Order cannot be determined from the chemical equation.

Consider this chemical reaction:

A + B -> C + D

To find the order wrt reactant A, we will have to conduct expts keeping B constant and varying [A] to monitor the effect on rate. Likewise, to find the order wrt B, we will need to keep A constant and vary [B]. One of the ways to keep the other [reactant] constant is to make it in large excess.

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