First Order Reactions – Class 12 | Chapter – 4 | Chemistry Short Notes Series PDF for NEET & JEE

First Order Reactions: A first order reaction is a type of chemical reaction where the rate of the reaction is directly proportional to the concentration of a single reactant. This means that the rate of the reaction increases as the concentration of the reactant increases, and decreases as the concentration of the reactant decreases.

First Order Reactions

Mathematically, a first order reaction can be expressed as:

Rate = k[A]

Where,

  • “k” is the rate constant of the reaction
  • “[A]” is the concentration of the reactant.
  • The units of k depend on the overall reaction order, while the units of [A] depend on the stoichiometry of the reaction.

In practical terms, a first-order reaction can be recognized by a exponential relationship between the concentration of the reactant and time. This means that the concentration of the reactant decreases exponentially over time, as the reaction proceeds.

Examples of first-order reactions include the radioactive decay of isotopes, the hydrolysis of esters, and the decomposition of hydrogen peroxide in the presence of a catalyst. In these reactions, the rate of the reaction is directly proportional to the concentration of the reactant, and can be described by a simple exponential decay function.


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By Team Learning Mantras