Question 1

The unit of rate constant for a zero-order reaction is:

Accepted Answer

For a zero-order reaction, the rate of reaction is independent of the concentration of reactants. Therefore, Rate = $kA^0 = k$. The unit of rate is concentration per unit time ($mol\cdot L^{-1}\cdot s^{-1}$), which directly gives the unit of the rate constant $k$.

Question 2

The minimum energy required for reactant molecules to undergo a chemical reaction is called:

Accepted Answer

Activation energy ($Ea$) is defined as the minimum extra amount of energy absorbed by reactant molecules so that their energy becomes equal to threshold energy and they can successfully form products.

Question 3

The half-life period ($t{1/2}$) of a first-order reaction is:

Accepted Answer

For a first-order reaction, the integrated rate equation gives $t{1/2} = \frac{0.693}{k}$. It is independent of the initial concentration of the reactants.

Question 4

According to the Arrhenius equation, the rate constant $k$ is expressed as:

Accepted Answer

The Arrhenius equation is given by $k = A e^{-Ea / RT}$, where $A$ is the Arrhenius factor (frequency factor), $Ea$ is activation energy, $R$ is gas constant, and $T$ is temperature.

Question 5

Molecularity of a reaction can never be:

Accepted Answer

Molecularity is the number of reacting species colliding simultaneously in an elementary reaction. It can never be zero, fractional, or negative, and it is generally not greater than three.

Chemical Kinetics — NCERT Class 12 Chemistry Important Questions & Revision Notes