Concentration dependence of rate is called differential rate equation. Integrated differential equations give relation between directly measured experimental data i.e., concentration at different times and rate constant. The integrated rate equations are different for the reactions of differennt reaction orders. the first-order reaction has a rate constant `1.15xx10^(-3)s^(-1)`.
Q. Under which condition a bimolecular reaction is kinetically first order reaction:

Options

A. When two ractants are involved.
B. When one of the reactants is in excess.
C. When one of the reactants does not involve in reaction.
D. None of these.

Explanation

To determine under which condition a bimolecular reaction behaves as a first-order reaction, we can follow these steps:

### Step 1: Understand the Reaction Order
A bimolecular reaction typically involves two reactants. The rate of the reaction can be expressed as:
\[ \text{Rate} = k[A][B] \]
where \( k \) is the rate constant, and \( [A] \) and \( [B] \) are the concentrations of the reactants.

### Step 2: Identify the Condition for Pseudo First Order
For a bimolecular reaction to behave as a first-order reaction, one of the reactants must be in excess. This means that the concentration of one reactant remains relatively constant throughout the reaction.

### Step 3: Simplify the Rate Equation
If we assume that reactant \( B \) is in excess, its concentration can be treated as a constant. Thus, we can rewrite the rate equation as:
\[ \text{Rate} = k[A][B] \approx k' [A] \]
where \( k' = k[B] \) is a new rate constant that incorporates the constant concentration of \( B \).

### Step 4: Conclusion
Since the rate now depends only on the concentration of \( A \), the reaction behaves as a first-order reaction with respect to \( A \). This condition, where one reactant is in excess, is known as a **pseudo first-order reaction**.

### Final Answer
A bimolecular reaction is kinetically first-order when one of the reactants is in excess.

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