CUET Preparation Today
Read the passage carefully and answer the Questions. The concentration dependence of the rate of a reaction is called the differential rate equation. It is not always convenient to determine the instantaneous rate, as it is measured by calculating the slope of the tangent at point 't' in the concentration vs time plot. This makes it difficult to determine the rate and hence the order of the reaction. This difficulty is overcome by integrating the differential rate equation. This integrated rate equation gives a direct relation between concentrations at different times and the rate constant. The integrated rate equations are different for the reactions having different reaction orders. |
Choose the correct statement regarding kinetics of a chemical reaction. |
The unit of rate constant for a second order reaction is $L\, mol^{-1}\, s^{-2}$. For complex reactions, order is given by the slowest step and the molecularity of the slowest step is the same as the order of the overall reaction. For zero order reaction, $t_{1/2}$ is independent of the initial concentration of the reactant. Decomposition of $N_2O_5$ is an example of pseudo first order reaction. |
For complex reactions, order is given by the slowest step and the molecularity of the slowest step is the same as the order of the overall reaction. |
The correct answer is Option (2) → For complex reactions, order is given by the slowest step and the molecularity of the slowest step is the same as the order of the overall reaction. ** Concept Used: • Order in complex reactions depends on rate-determining step • Zero order half-life depends on initial concentration • Second order rate constant unit = L mol⁻¹ s⁻¹ Explanation: Option 1: The unit of rate constant for a second order reaction is L mol⁻¹ s⁻² Incorrect Correct unit is: L mol⁻¹ s⁻¹ Not s⁻² Option 2: For complex reactions, order is given by the slowest step and the molecularity of the slowest step is the same as the order of the overall reaction Correct In multi-step reactions, the rate-determining step (slowest step) controls the reaction rate, and its molecularity corresponds to the overall order. Option 3: For zero order reaction, t₁/₂ is independent of the initial concentration of the reactant Incorrect For zero order reaction: t₁/₂ = [R]₀ / 2k Hence depends on initial concentration. Option 4: Decomposition of N₂O₅ is an example of pseudo first order reaction Incorrect Decomposition of N₂O₅ is a true first order reaction. |
