Comprehension
Read the passage carefully and answer the questions that follow.
Passage: The rate of a chemical reaction is expressed either in terms of decrease in the concentration of reactants or increase in the concentration of a product per unit time. Rate of the reaction depends upon the nature of reactants, concentration of reactants, temperature, presence of catalyst, surface area of the reactants and presence of light. Rate of reaction is directly related to the concentration of reactant. Rate law states that the rate of reaction depends upon the concentration terms on which the rate of reaction actually depends, as observed experimentally. The sum of powers of the concentration of the reactants in the Rate law expression is called order of reaction while the number of reacting species taking part in an elementary reaction which must collide simultaneously in order to bring about a chemical reaction is called molecularity of the reaction.
Answer the following questions:
Passage: The rate of a chemical reaction is expressed either in terms of decrease in the concentration of reactants or increase in the concentration of a product per unit time. Rate of the reaction depends upon the nature of reactants, concentration of reactants, temperature, presence of catalyst, surface area of the reactants and presence of light. Rate of reaction is directly related to the concentration of reactant. Rate law states that the rate of reaction depends upon the concentration terms on which the rate of reaction actually depends, as observed experimentally. The sum of powers of the concentration of the reactants in the Rate law expression is called order of reaction while the number of reacting species taking part in an elementary reaction which must collide simultaneously in order to bring about a chemical reaction is called molecularity of the reaction.
Answer the following questions:
Question: 1
What is a rate determining step?
What is a rate determining step?
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In a reaction mechanism, the rate-determining step controls the speed of the overall reaction because it is the slowest step in the process.
Updated On: Feb 28, 2025
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Solution and Explanation
The rate-determining step is the slowest step in a reaction mechanism. It limits the overall rate of the reaction because the rate of the entire reaction is governed by the rate of this step. In a multi-step reaction, the rate-determining step is the step with the highest activation energy or the slowest rate.
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Question: 2
Define complex reaction.
Define complex reaction.
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Complex reactions involve multiple elementary steps, each with its own reaction rate, leading to the overall reaction.
Updated On: Feb 28, 2025
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Solution and Explanation
A complex reaction involves more than one elementary reaction step. These reactions occur through a sequence of individual reactions, each involving the collision and interaction of reactants. A complex reaction can have multiple intermediates and may involve different molecular species at various stages.
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Question: 3
What is the effect of temperature on the rate constant of a reaction?
What is the effect of temperature on the rate constant of a reaction?
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An increase in temperature results in an increase in the rate constant, accelerating the reaction.
Updated On: Feb 28, 2025
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Solution and Explanation
The rate constant of a reaction generally increases with temperature. This is explained by the Arrhenius equation, which shows that the rate constant \(k\) increases exponentially with an increase in temperature. As the temperature rises, the number of molecules having sufficient energy to overcome the activation energy barrier increases, leading to an increase in the rate constant.
\[ k = A \cdot e^{-\frac{E_a}{RT}} \]
Where:
- \(k\) is the rate constant,
- \(A\) is the frequency factor,
- \(E_a\) is the activation energy,
- \(R\) is the gas constant,
- \(T\) is the temperature in Kelvin.
\[ k = A \cdot e^{-\frac{E_a}{RT}} \]
Where:
- \(k\) is the rate constant,
- \(A\) is the frequency factor,
- \(E_a\) is the activation energy,
- \(R\) is the gas constant,
- \(T\) is the temperature in Kelvin.
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Question: 4
Why is molecularity applicable only for elementary reactions whereas order is applicable for elementary as well as complex reactions?
Why is molecularity applicable only for elementary reactions whereas order is applicable for elementary as well as complex reactions?
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Molecularity applies only to elementary reactions, while order applies to the overall reaction, regardless of whether it is elementary or complex.
Updated On: Feb 28, 2025
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Solution and Explanation
Molecularity refers to the number of reacting species involved in an elementary reaction and is a property of that specific step. It applies only to elementary reactions because these reactions occur in a single step and involve a fixed number of reacting molecules. On the other hand, the order of a reaction is determined experimentally and refers to the relationship between the concentration of reactants and the rate of the overall reaction, which can apply to both elementary and complex reactions.
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Question: 5
The conversion of molecule X to Y follows second-order kinetics. If the concentration of X is increased 3 times, how will it affect the rate of formation of Y?
The conversion of molecule X to Y follows second-order kinetics. If the concentration of X is increased 3 times, how will it affect the rate of formation of Y?
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In a second-order reaction, the rate of the reaction is proportional to the square of the concentration of the reactant.
Updated On: Feb 28, 2025
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Solution and Explanation
For a second-order reaction, the rate of the reaction is proportional to the square of the concentration of reactant \(X\):
\[
\text{Rate} = k \cdot [X]^2
\]
If the concentration of \(X\) is increased 3 times, the rate of formation of \(Y\) will increase by a factor of: \[ \left( 3 \right)^2 = 9 \]
Thus, the rate of formation of \(Y\) will increase by a factor of 9 when the concentration of \(X\) is increased 3 times.
If the concentration of \(X\) is increased 3 times, the rate of formation of \(Y\) will increase by a factor of: \[ \left( 3 \right)^2 = 9 \]
Thus, the rate of formation of \(Y\) will increase by a factor of 9 when the concentration of \(X\) is increased 3 times.
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Top Questions on Chemical Kinetics
Rate law for a reaction between $A$ and $B$ is given by $\mathrm{R}=\mathrm{k}[\mathrm{A}]^{\mathrm{n}}[\mathrm{B}]^{\mathrm{m}}$. If concentration of A is doubled and concentration of B is halved from their initial value, the ratio of new rate of reaction to the initial rate of reaction $\left(\frac{\mathrm{r}_{2}}{\mathrm{r}_{1}}\right)$ is
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B. The unit of A is same as that of k in Arrhenius equation.
C. At a given temperature, a low activation energy means a fast reaction.
D. A and Ea as used in Arrhenius equation depend on temperature.
E. When Ea >> RT. A and Ea become interdependent.
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