Consider the following statements about the rate of a reaction.
(A) The rate law of a reaction is also called the rate equation or rate expression.
(B) Rates of reactions generally increase when the concentrations of the reactants increase.
(C) The precipitation of silver chloride on mixing aqueous solutions of silver nitrate and sodium chloride is a very slow reaction.
(D) The average rate of a reaction is determined to express the rate at a particular moment of time.
Which of the statements given above are correct? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A) and (B) only
The rate of a reaction depends on the concentration of the reactants, and the way it depends is written as the rate law. Rates also differ greatly from one reaction to another, and the rate at one moment differs from the rate averaged over an interval.
(A) The rate law of a reaction is also called the rate equation or rate expression. — True. These are the three names for the same expression.
(B) Rates of reactions generally increase when the concentrations of the reactants increase. — True. This is also why a rate falls with time, as the reactants are used up.
(C) The precipitation of silver chloride on mixing aqueous solutions of silver nitrate and sodium chloride is a very slow reaction. — False. It is an ionic reaction that occurs instantaneously; rusting of iron is an example of a very slow reaction.
(D) The average rate of a reaction is determined to express the rate at a particular moment of time. — False. The average rate is constant over its whole time interval; the rate at a particular moment is the instantaneous rate.
NCERT (2026-27 edition):
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. It is also called as rate equation or rate expression.”
3.2.2 Rate Expression and Rate Constant – “…Conversely, rates generally increase when reactant concentrations increase.”
3.1 Rate of a Chemical Reaction – “Some reactions such as ionic reactions occur very fast, for example, precipitation of silver chloride occurs instantaneously by mixing of aqueous solutions of silver nitrate and sodium chloride.”
“However, average rate cannot be used to predict the rate of a reaction at a particular instant as it would be constant for the time interval for which it is calculated. So, to express the rate at a particular moment of time we determine the instantaneous rate.”