Consider the following statements about the rate of a chemical reaction.
(A) The rate of a reaction depends upon experimental conditions such as the concentration of reactants (pressure in case of gases), temperature and catalyst.
(B) The representation of the rate of a reaction in terms of the concentration of the products is known as the rate law.
(C) In a rate law, the proportionality constant k is called the rate constant.
(D) The expressions \( -\frac{\Delta[R]}{\Delta t} \) and \( +\frac{\Delta[P]}{\Delta t} \) represent the instantaneous rate of a reaction.
Which of the statements given above are correct? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A) and (C) only
The rate of a reaction is the change in concentration of a reactant or product in unit time. How it depends on the concentrations of the reactants is written as the rate law.
(A) The rate of a reaction depends upon experimental conditions such as the concentration of reactants (pressure in case of gases), temperature and catalyst. — True. These are the factors that change the rate of a reaction.
(B) The representation of the rate of a reaction in terms of the concentration of the products is known as the rate law. — False. The rate law expresses the rate in terms of the concentration of the reactants.
(C) In a rate law, the proportionality constant k is called the rate constant. — True. In Rate = k[A]x[B]y, k is the rate constant.
(D) The expressions −Δ[R]/Δt and +Δ[P]/Δt represent the instantaneous rate of a reaction. — False. A change Δ over a time interval Δt gives the average rate. The instantaneous rate is −d[R]/dt or d[P]/dt, taken as Δt approaches zero.
NCERT (2026-27 edition):
3.2 Factors Influencing Rate of a Reaction – “Rate of reaction depends upon the experimental conditions such as concentration of reactants (pressure in case of gases), temperature and catalyst.”
3.2.1 Dependence of Rate on Concentration – “…The representation of rate of reaction in terms of concentration of the reactants is known as rate law.”
3.2.2 Rate Expression and Rate Constant – “This form of equation (3.4 b) is known as differential rate equation, where k is a proportionality constant called rate constant.”
3.1 Rate of a Chemical Reaction – “Equations (3.1) and (3.2) given above represent the average rate of a reaction, rav.”
\( \displaystyle \text{Rate of disappearance of R} = -\frac{\Delta[\text{R}]}{\Delta t} \quad (3.1) \qquad \text{Rate of appearance of P} = +\frac{\Delta[\text{P}]}{\Delta t} \quad (3.2) \)