Consider the following statements:
(A) The rate of a reaction is directly proportional to its Gibbs energy change.
(B) The order of an elementary reaction can be found from its balanced chemical equation.
(C) In a first-order reaction, the concentration of the reactant decreases exponentially with time.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (B) and (C) only
(A) The rate of a reaction is directly proportional to its Gibbs energy change. — False. ΔG is a thermodynamic quantity: it tells only whether a reaction is feasible, not how fast it goes.
(B) The order of an elementary reaction can be found from its balanced chemical equation. — True. An elementary reaction takes place in one step, so its equation shows the species that collide. For such a reaction the order equals the molecularity, read from the equation.
(C) In a first-order reaction, the concentration of the reactant decreases exponentially with time. — True. The integrated rate equation of a first-order reaction gives \( [\mathrm{R}]=[\mathrm{R}]_0e^{-kt} \): [R] falls exponentially with time.
NCERT (2026-27 edition):
Unit 3 Chemical Kinetics – “… Thermodynamics tells only about the feasibility of a reaction whereas chemical kinetics tells about the rate of a reaction.”
Summary – “… Molecularity and order of an elementary reaction are same.”
3.3.2 First Order Reactions – “… Taking antilog of both sides”
\( \displaystyle [\mathrm{R}]=[\mathrm{R}]_0\,e^{-kt} \qquad (3.14) \)