Question 14 Marks
(a) Define molecularity of the reaction-
(b) Explain the effect of the presence of a catalyst on the rate of reaction.
(c) In a first order reaction at 300 k the initial quantity of the reactant was $1.0 X ^{-2} molL ^{-1}$ which reduced to $0.5 \times 10^{-2} molL ^{-1}$ in 30 minutes Calculate the rate constant of the reaction at 300 k .
(b) Explain the effect of the presence of a catalyst on the rate of reaction.
(c) In a first order reaction at 300 k the initial quantity of the reactant was $1.0 X ^{-2} molL ^{-1}$ which reduced to $0.5 \times 10^{-2} molL ^{-1}$ in 30 minutes Calculate the rate constant of the reaction at 300 k .
Answer
View full question & answer→(a) Definition of Molecularity
Molecularity of a reaction is defined as the total number of atoms, ions, or molecules of reactants that must collide simultaneously in an elementary (single-step) reaction to result in a chemical change. It is always a theoretical value, a positive whole number, and cannot be zero or fractional.
(b) Effect of Catalyst on Rate of Reaction
A catalyst increases the rate of a chemical reaction without undergoing any permanent chemical change itself. It functions by providing an alternative reaction pathway that has a lower activation energy ( $E_a$ ) compared to the uncatalyzed reaction.
By lowering the activation energy barrier, a larger fraction of reactant molecules possess sufficient energy to cross the threshold and form products, thereby significantly increasing the reaction velocity.
(c) Numerical Calculation
Given:
- Temperature ( $T$ ): 300 K (Constant)
- Initial Concentration $\left([A]_0\right): 1.0 \times 10^{-2} mol L ^{-1}$
- Final Concentration $([A]): 0.5 \times 10^{-2} mol L ^{-1}$
- Time $(t)$ : 30 minutes
Observation: Notice that the final concentration is exactly half of the initial concentration ( 0.5 is half of 1.0$)$. This means the given time $(30 min)$ is the half-life $\left(t_{1 / 2}\right)$ of the reaction.
Formula for First Order Rate Constant:
$k=\frac{0.693}{t_{1 / 2}}$
Calculation:
$\begin{array}{c}k=\frac{0.693}{30 min} \\ k=0.0231 min^{-1}\end{array}$
In Scientific Notation:
$k=2.31 \times 10^{-2} min^{-1}$
The rate constant of the reaction at 300 K is $2.31 \times 10^{-2} min^{-1}$.
Would you like me to show you how to convert this rate constant into seconds $\left(s^{-1}\right)$ or explain the difference between Order and Molecularity?
Molecularity of a reaction is defined as the total number of atoms, ions, or molecules of reactants that must collide simultaneously in an elementary (single-step) reaction to result in a chemical change. It is always a theoretical value, a positive whole number, and cannot be zero or fractional.
(b) Effect of Catalyst on Rate of Reaction
A catalyst increases the rate of a chemical reaction without undergoing any permanent chemical change itself. It functions by providing an alternative reaction pathway that has a lower activation energy ( $E_a$ ) compared to the uncatalyzed reaction.
By lowering the activation energy barrier, a larger fraction of reactant molecules possess sufficient energy to cross the threshold and form products, thereby significantly increasing the reaction velocity.
(c) Numerical Calculation
Given:
- Temperature ( $T$ ): 300 K (Constant)
- Initial Concentration $\left([A]_0\right): 1.0 \times 10^{-2} mol L ^{-1}$
- Final Concentration $([A]): 0.5 \times 10^{-2} mol L ^{-1}$
- Time $(t)$ : 30 minutes
Observation: Notice that the final concentration is exactly half of the initial concentration ( 0.5 is half of 1.0$)$. This means the given time $(30 min)$ is the half-life $\left(t_{1 / 2}\right)$ of the reaction.
Formula for First Order Rate Constant:
$k=\frac{0.693}{t_{1 / 2}}$
Calculation:
$\begin{array}{c}k=\frac{0.693}{30 min} \\ k=0.0231 min^{-1}\end{array}$
In Scientific Notation:
$k=2.31 \times 10^{-2} min^{-1}$
The rate constant of the reaction at 300 K is $2.31 \times 10^{-2} min^{-1}$.
Would you like me to show you how to convert this rate constant into seconds $\left(s^{-1}\right)$ or explain the difference between Order and Molecularity?