Question

For which of the following order unit of rate of reaction and rate constant are the same?

• A. First-order reaction
• B. Second-order reaction
• C. Third-order recation
• D. Zero-order reaction

Answer 1

The correct option is D

Zero-order reaction

The explanation for the correct answer:-

Option (D) Zero-order reaction:-

1. A zero-order reaction is one in which the rate of the reaction remains constant while the concentration of the reactant changes.
2. Because the rate of these reactions is proportional to the zeroth power of reactant concentration, the rate constant of these reactants is always equal to the rate constant of the specific processes.
3. Unit of rate constant:$\mathrm{mol}/\mathrm{L}/\mathrm{t}$
4. Unit of zero-order reaction: $\mathrm{mol}/\mathrm{L}/\mathrm{t}$

The explanation for incorrect answer(s):

Option (A) First-order reaction:-

1. The first-order reaction has a rate of reaction that is proportional to the reactant concentration.
2. Rate law, $\mathrm{r}=\mathrm{k}{\left[\mathrm{A}\right]}^1$, $\mathrm{k}=\frac{\mathrm{r}}{\left[\mathrm{A}\right]}$ $=\frac{\mathrm{mol}\times 1^{-1}\times {\mathrm{s}}^{-1}}{\mathrm{mol}\times 1^{-1}}={\mathrm{s}}^{-1}$
3. Hence the units are not the same it is an incorrect answer.

Option (B) Second-order reaction:-

1. When the order of the reaction is 2, the reaction is considered second-order.
2. The rate of these reactions can be calculated using either the concentration of one reactant squared or the concentration of two reactants separately.
3. Rate law$=\mathrm{k}{\left[\mathrm{A}\right]}^2$$=\mathrm{L}{\mathrm{mol}}^{-1}{\sec }^{-1}$.
4. Hence the units are not the same it is an incorrect answer.

Option (C) Third-order reaction:-

1. A chemical reaction of third order is one in which the rate of reaction is proportional to the concentration of each reacting molecule.
2. The rate is usually defined by the variation of three concentration components in this reaction.
3. Rate law$=\mathrm{K}{\left[\mathrm{A}\right]}^{\mathrm{x}}{\left[\mathrm{B}\right]}^{\mathrm{y}}{\left[\mathrm{C}\right]}^{\mathrm{z}}$$={\mathrm{L}}^2{\mathrm{mol}}^{-2}{\mathrm{s}}^{-1}$.
4. Hence, the units are not the same it is an incorrect answer.

Therefore, Zero-order reactions have the same units of rate constant and order unit of rate of reaction and hence option D is correct.