Question

Which one of the following is incorrect?

• A. Rate constant equals the rate of reaction when concentration of reactants equals unity.
• B. Larger the value of rate constant (\(k\)) value faster is the chemical reaction.
• C. The unit for rate constant for \(n^{th}\) order reaction is \((\text{mol/L}^{-1} \text{s}^{-1})^{n-1}\).
• D. The value of rate constant (\(k\)) is independent of concentration of reactants.

Hint:

The unit of the rate constant depends on the order of the reaction. For a first-order reaction, it is \( \text{s}^{-1} \), and for a second-order reaction, it is \( \text{L/mol} \cdot \text{s} \).

Answer 1

The Correct Option is C

Step 1: Analyze statement A.
The rate constant equals the rate of reaction when the concentration of reactants equals unity. This is true. The rate law is \( \text{Rate} = k[A]^n \), and when \( [A] = 1 \), the rate constant \( k \) equals the rate of reaction.

Step 2: Analyze statement B.
Larger the value of rate constant (\(k\)), faster is the chemical reaction. This is also true. A higher rate constant indicates a faster reaction.

Step 3: Analyze statement C.
The unit for rate constant for \( n^{th} \) order reaction is \((\text{mol/L}^{-1} \text{s}^{-1})^{n-1}\). This statement is incorrect. The correct unit for the rate constant depends on the order of the reaction and is given by:
\[ k = \frac{\text{Rate}}{[\text{A}]^n} \]
For a first-order reaction, the unit of \( k \) is \( \text{s}^{-1} \), for a second-order reaction, it is \( \text{L/mol} \cdot \text{s} \), etc. The unit is not as described in the statement.

Step 4: Analyze statement D.
The value of rate constant (\(k\)) is independent of concentration of reactants. This is true. The rate constant is only dependent on temperature and not on the concentration of reactants.

Step 5: Conclusion.
Since statement C is incorrect, the correct answer is option (C).