Question

Which of the following statements about zero order reaction is/are not true?

• A. Unit of rate constant is $se{c}^{-1}$.
• B. The graph between log (reactant) versus time is a straight line.
• C. The rate of reaction increases with the increase in concentration of reactants.
• D. Rate of reaction is independent of concentration of reactants.

Answer 1

Answer: (A), (B), (C)

Unit of rate constant is $se{c}^{-1}$.
The rate of reaction increases with the increase in concentration of reactants.
The graph between log (reactant) versus time is a straight line.

Let us consider a zero order reaction:

$A\to B$

Rate Law for Zero Order Reaction is given as :

$Rate=-\frac{d\left[A\right]}{dt}=k[A{]}^0=k$

where k is Rate Constant

Hence, The unit of rate constant is the unit of Rate of Reaction i.e. $mollitr{e}^{-1}se{c}^{-1}$

$\because -\frac{d\left[A\right]}{dt}=k$

$⟹\left[A\right]=\left[A_0\right]-kt$ . . . . (1)

where $\left[A_0\right]$ is the initial concentration of Reactant A.

taking log in the equation (1), we get,

$log\left[A\right]=log\left[A_0\right]-log\left[kt\right]$ . . . . (2)

$\because \left(2\right)isnotofformlog\left[A\right]=mt.\therefore \text{The graph between log[Reactant] versus time is not a straight line.}$

$\because \text{Rate of Zero order reaction is equal to Rate constant of that reaction, which is independent of concentration of reactant.}$

Hence, on increasing concentration of reactants, rate of reaction does not increase.

From Rate Law for Zero Order reaction, we can conclude that rate of reaction is independent of concentration of reactants.

Hence, Option $"A","B"\&"C"$are not true.