Chemistry class 12th Order_of_Reaction

Order of a Reaction


In chemical kinetics, the order of a reaction indicates the dependence of the reaction rate on the
concentration of reactants. It is determined experimentally and helps in understanding the reaction
mechanism.


Types of Reaction Orders:

Zero Order Reaction
Rate is independent of reactant concentration: Rate = k

First Order Reaction
Rate depends on one reactant: Rate = k[A]

Second Order Reaction
Rate depends on one or two reactants: Rate = k[A]^2 or k[A][B]

Fractional & Mixed Order
Involves non-integer or varying orders in the reaction mechanism.

Determination of Reaction Order:

1. Method of Initial Rates - Measuring initial reaction rates at different concentrations.
2. Integrated Rate Laws - Comparing concentration vs. time data.
3. Graphical Method - Plotting graphs like [A] vs. time, ln[A] vs. time, etc.
4. Half-Life Method - Checking if half-life is constant (First order) or varies.


Mathematical Expressions & Graphs:

For a reaction A -> Products:
- Zero Order: [A] = [A]0 - kt
- First Order: ln[A] = ln[A]0 - kt
- Second Order: 1/[A] = 1/[A]0 + kt


Graphs of these equations help identify reaction order.


Examples & Applications: