Order of Reaction

In the rate equation, we know,

Rate = k [A]^x [B]^y

Where x and y indicate how sensitive the rate is to the change in concentration of A and B.

The sum of these exponents, i.e., x + y gives the overall order of a reaction whereas x and y represent the order concerning the reactants A and B respectively.

Read More about Order of Reaction.

Different types of chemical reactions are categorized based on how the rate of the reaction depends on the concentration of the reactants:

• Zeor Order Reactions
• First-Order Reactions
• Pseudo-First Order Reactions
• Second Order Reactions

Let’s discuss these types in brief as follows:

Zero Order Reactions

The rate of reaction in these reactions is unaffected by the concentration of the reactants. Changes in the concentration of the reactants do not impact the reaction speed.

• Example: Enzyme-catalyzed oxidation of ethanol (CH₃CH₂OH) to acetaldehyde (CH₃CHO).

First-Order Reactions

The rates of these reactions depend on the concentration of only one reactant (order of reaction is 1). Even if multiple reactants are present, only one reactant has a first-order concentration, while the others have zero-order concentration.

• Example: 2H₂O₂ → 2H₂O + O₂.

Read more about First Order Reaction.

Pseudo-First Order Reactions

In pseudo-first-order reactions, one reactant’s concentration remains constant and is included in the rate constant in the rate expression. This constant concentration may be due to an excess compared to other reactants or because it acts as a catalyst.

• Example: CH₃COOCH₃ + H₂O → CH₃COOH + CH₃OH (pseudo-first order kinetics due to excess water).

Read more about Pseudo First Order Reaction.

Second-Order Reaction

A second-order reaction has an order of 2. The rate of these reactions can be expressed as the square of the concentration of one reactant or as the product of the concentrations of two separate reactants.

• Example: r = k[A]² or r = k[A][B], e.g., NO₂+ CO → NO + CO₂

Chemical Kinetics is a part of physical chemistry that focuses on the rate of chemical reactions and the reasons behind them. It involves figuring out the speed and details of chemical reactions, studying the factors that affect how fast they happen, and how molecules interact during these changes.

This field is important in various scientific areas, from improving industrial processes to understanding complicated reactions in biological systems. By focusing on how molecules interact, chemical kinetics helps us to understand the complex movements of atoms and molecules in the world of chemistry.