Problem 45 - A Complete Resource Book in Chemistry for JEE Main

Question

A catalyst increases rate of reaction by (a) decreasing enthalpy (b) decreasing activation energy (c) decreasing internal energy (d) increasing activation energy

Step-by-Step Solution

Answer

The correct answer is (b) decreasing activation energy.

Step 1: Analyze the Role of a Catalyst

A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. It achieves this by providing an alternative reaction pathway with a lower activation energy.

Step 2: Examine the Options

We are given four options to choose from. Let's consider each: - (a) Decreasing enthalpy: Enthalpy change is a measure of the overall heat change in a reaction and is not influenced by the presence of a catalyst. - (b) Decreasing activation energy: Catalysts work by lowering the activation energy, making it easier for the reactants to form products. - (c) Decreasing internal energy: Internal energy is the total energy within the system, which is not directly altered by a catalyst. - (d) Increasing activation energy: Increasing activation energy would actually slow down the reaction, the opposite effect of a catalyst.

Step 3: Identify the Correct Option

Considering the roles and effects explained, the correct option is (b) Decreasing activation energy, as this is how a catalyst increases the reaction rate.

Key Concepts

Activation Energy

Activation energy is the minimum amount of energy that reactant molecules need to possess in order to successfully collide and form products. This concept is crucial because it determines whether a reaction will occur spontaneously or requires additional input of energy.
Think of it as a hurdle that reactants must overcome to transform into products. If the activation energy is high, the reaction rate will generally be slower because fewer molecules will have enough energy to clear this hurdle.

• Activation energy is represented by the symbol \( E_a \).
• It acts as a barrier that must be overcome for a reaction to proceed.

Catalysts play a key role in altering activation energy, which brings us to our next topic.

Reaction Rate

The reaction rate measures how quickly a chemical reaction progresses. It can be expressed in terms of the concentration of reactants consumed or the concentration of products formed over time. Various factors can influence reaction rate, such as temperature, concentration, and the presence of a catalyst.
A higher reaction rate implies that reactants are being converted into products faster. Catalysts are one of the most effective ways to increase the reaction rate without changing the conditions like temperature or concentration.

• Catalysts accelerate reaction rates by providing an easier path with lower activation energy.
• This allows more frequent and successful collisions between reactant molecules.

It's fascinating how catalysts can make reactions happen faster, making them invaluable in both industrial and biological processes.

Alternative Reaction Pathway

An alternative reaction pathway describes a different route that a chemical reaction may take when a catalyst is present. This alternative pathway has a lower activation energy, making it easier for the reaction to proceed.
While the overall reactants and products remain the same, the steps involved in getting there can be altered.

• Catalysts essentially provide a shortcut for the reaction, bypassing the higher energy pathway.
• Despite the change in pathway, the catalyst remains unchanged after the reaction concludes.

Understanding alternative reaction pathways helps chemists design more efficient reactions, saving energy and resources in the process.