Problem 69 - A Complete Resource Book in Chemistry for JEE Main

Question

A catalyst in a chemical reaction (a) decreases rate constant of the reaction (b) reduces enthalpy of the reaction (c) does not affect equilibrium constant of the reaction (d) increases activation energy of the reaction

Step-by-Step Solution

Answer

(c) does not affect equilibrium constant of the reaction.

Step 1: Identify the Role of a Catalyst

A catalyst is a substance that speeds up a chemical reaction without being consumed by the reaction itself. It achieves this by providing an alternative pathway for the reaction with a lower activation energy.

Step 2: Assess the Options

Let's evaluate each option based on the role of a catalyst: (a) Catalysts increase the rate constant of the reaction, they don't decrease it. (b) Catalysts don't alter the enthalpy of the reaction; they simply alter the rate. (c) Catalysts do not affect the equilibrium constant of a reaction; they help the system reach equilibrium faster. (d) Catalysts decrease the activation energy, not increase it. The lower activation energy speeds up the reaction.

Step 3: Select the Correct Statement

Among the given options, the correct statement regarding a catalyst is that it does not affect the equilibrium constant. Therefore, option (c) is the correct answer.

Key Concepts

Activation Energy

Activation energy is the minimum amount of energy required for a chemical reaction to occur. Think of it as the energy barrier that reactants must overcome to transform into products. A higher activation energy means that fewer molecules have sufficient energy to react when they collide, thereby slowing down the reaction rate.

Catalysts play a significant role in modifying the activation energy of a reaction. By providing an alternative reaction pathway, catalysts effectively lower the activation energy, meaning that more molecules can surpass the energy barrier to react. This is why reactions happen faster in the presence of a catalyst.

• Activation energy is crucial in determining the reaction rate.
• Catalysts lower the activation energy.
• Lower activation energy leads to a higher reaction rate.

This concept is especially important in industrial and biological reactions, where catalysts are used to enhance the speed of chemical processes.

Equilibrium Constant

In a chemical reaction at equilibrium, the concentrations of the reactants and products remain constant over time. The equilibrium constant (\( K \) ) is a valuable metric that provides insight into the balance between these concentrations at equilibrium.

Importantly, a catalyst does not affect the equilibrium position or the equilibrium constant of a chemical reaction. It affects only the speed at which equilibrium is reached.

• Equilibrium constant (\( K \) ) indicates the ratio of product to reactant concentrations.
• A catalyst speeds up reaching equilibrium but does not change \( K \) .
• Equilibrium is about the ratio, not the absolute values of concentrations.

Understanding the unchanged nature of the equilibrium constant in the presence of a catalyst helps us appreciate how catalysts function—they enable faster attainment of equilibrium without altering the equilibrium itself.

Chemical Reaction Rate

The chemical reaction rate refers to the speed at which reactants are converted into products. Factors impacting this rate include temperature, concentration, and the presence of catalysts.

Catalysts increase the reaction rate by lowering the activation energy, allowing more molecules to participate in the reaction. Thus, even at the same temperature and concentrations, a catalyzed reaction proceeds faster than an uncatalyzed one.

• Reaction rate measures how quickly a reaction proceeds.
• Catalysts increase the reaction rate without being consumed.
• Lower activation energy from catalysts leads to more active collisions.

By understanding these principles, one can predict how adjustments in reaction conditions or the addition of a catalyst can modify the reaction rate, which is vital for optimizing chemical processes both in laboratories and industrial settings.