JEE Main & Advanced Chemistry Chemical Kinetics / रासायनिक बलगतिकी Law Of Mass Action And Rate Constant

The rate at which a substance reacts is directly proportional to its active mass and the rate at which a reaction proceeds is proportional to the product of the active masses of the reacting substances.

• For a reaction, \[aA+bB\to \] product

Rate \[=\left( \frac{dx}{dt} \right)\propto {{[A]}^{a}}{{[B]}^{b}}\]; \[\left( \frac{dx}{dt} \right)=k{{[A]}^{a}}{{[B]}^{b}}\]

Where k is called rate constant or velocity constant.

When \[[A]=[B]=1\ mol/litre\], then \[\frac{dx}{dt}=k\]

Thus, rate constant k is also called specific reaction rate.

• The value of rate constant depends on, nature of reactant, temperature and catalyst. It is independent of concentration of the reactants.
• Unit of rate constant \[={{\left[ \frac{\text{litre}}{\text{mol}} \right]}^{n-1}}\times {{\sec }^{-1}}\]\[\ ={{\left[ \frac{\text{mol}}{\text{litre}} \right]}^{1-n}}\times {{\sec }^{-1}}\]

  Where \[n=\] order of reaction.