Problem 35 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is correct about enzymes? (a) it reduces the activation energy (b) it increases the activation energy (c) it changes the equilibrium constant (d) none of these

Step-by-Step Solution

Answer

Option (a) is correct: enzymes reduce the activation energy.

Step 1: Understand Enzymes

Enzymes are biological catalysts that speed up chemical reactions in cells without being consumed in the process. To solve this question, we need to recall what enzymes do in terms of energy and equilibrium.

Step 2: Assess Activation Energy

Enzymes lower the activation energy required for a reaction to proceed. This is a key property of enzymes, allowing reactions to occur faster by lowering the energy barrier.

Step 3: Evaluate Effect on Equilibrium Constant

While enzymes speed up the rate of reaching equilibrium, they do not alter the equilibrium constant itself. The equilibrium position and constant depend on the relative energies of the reactants and products, not the pathway taken.

Step 4: Review Options

- (a) is correct because enzymes reduce the activation energy. - (b) is incorrect; enzymes do not increase activation energy. - (c) is incorrect; enzymes do not change the equilibrium constant. - (d) is incorrect since (a) is correct.

Key Concepts

Activation Energy

Activation energy is a concept in chemistry that refers to the minimum energy required to start a chemical reaction. Imagine activation energy as a hill that reactants must climb to transform into products.
Enzymes play a crucial role in biological systems by lowering the activation energy barrier. They don't change the overall energy balance, but they make it easier for reactions to occur by decreasing the energy required to reach the transition state.
Here's how enzymes lower activation energy:

• They provide an alternative reaction pathway with a lower energy barrier.
• The enzyme's active site perfectly fits the substrate, stabilizing the transition state.
• Activation energy reduction means reactions can proceed faster and more efficiently.

By lowering the activation energy, enzymes make it possible for essential biochemical reactions to take place at the temperatures and pressures found within living organisms.

Equilibrium Constant

The equilibrium constant, often represented as \( K_{eq} \), is a number that describes the balance point of a reaction. It tells us the ratio of the concentrations of products to reactants at equilibrium, reflecting how far a reaction will proceed.An important aspect to know is that while enzymes speed up reactions, they do not change the position of equilibrium.

• Equilibrium is a state where the forward and reverse reactions occur at the same rate.
• Enzymes hasten the attainment of equilibrium but the equilibrium constant \( K_{eq} \) remains unchanged.
• The value of \( K_{eq} \) is only dependent on the nature and temperature of the reactants and products, not on the enzyme.

This means that enzymes do not alter the equilibrium position. They simply help the system reach that position faster.

Biological Catalysts

Biological catalysts, or enzymes, are proteins that significantly enhance the speed of chemical reactions in biological systems without being consumed in the process.
Enzymes exhibit specificity, meaning each enzyme catalyzes a specific reaction, which is crucial for maintaining the complex order within cells.
Key features of biological catalysts include:

• Specificity: Each enzyme tends to be selective about the substrate it acts on.
• Efficiency: Enzymes are highly efficient, increasing reaction speeds by millions of times compared to reactions without them.
• Regulation: Enzyme activity can be regulated by factors such as temperature, pH, and the presence of inhibitors or activators.

By acting as biological catalysts, enzymes ensure that vital life processes like metabolism, DNA replication, and cellular respiration proceed at the rates necessary for life.