Rate equation of a zero order reaction

Rate Equation of a Zero Order Reaction

A zero order reaction is a type of chemical reaction in which the rate of reaction is independent of the concentration of the reactants. The reaction rate stays unchanged throughout the process until all reactants are used up.

Definition

In zero-order reactions, the reaction rate remains unaffected by variations in reactant concentration. It is mathematically represented as:

Rate = k

Where k is the rate constant with units of \(mol·L^{-1}·s^{-1}\).

Integrated Rate Law

The integrated form of the zero order rate equation is:

[A] = [A]₀ - kt

Where:

• [A] is the concentration of the reactant at time t.
• [A]₀ is the initial concentration of the reactant.
• k is the rate constant.
• t is the time elapsed.

Graphical Representation

A plot of [A] versus time (t) gives a straight line with a negative slope equal to –k and a y-intercept of [A]₀.

Units of Rate Constant

Since rate is constant, the units of k in a zero order reaction are:

\(mol·L^{-1}·s^{-1}\)

Characteristics of Zero Order Reactions

• The rate of the reaction remains unchanged as the reaction proceeds.
• Reactant concentrations have no influence on the reaction rate.
• Common in reactions where a catalyst or surface is saturated.

Examples

• Decomposition of ammonia on a platinum surface.
• Photochemical decomposition of HI in the presence of light.

Zero order reactions are important in understanding reaction mechanisms, especially in catalysis and surface chemistry. Their unique property of rate independence from reactant concentration makes them useful for kinetic analysis.