Problem 59 - General Chemistry: Principles and Modern Applications

Question

The following statements about catalysis are not stated as carefully as they might be. What slight modifications would you make in them? (a) A catalyst is a substance that speeds up a chemical reaction but does not take part in the reaction. (b) The function of a catalyst is to lower the activation energy for a chemical reaction.

Step-by-Step Solution

Answer

Refined versions of the statements are: (a) A catalyst is a substance that speeds up a chemical reaction by participating in the reaction but is returned to its initial state at the end of the reaction and (b) The function of a catalyst is to provide an alternate pathway for the chemical reaction that has a lower activation energy.

Step 1: Analyze Statement A

Analyze the first assertion: 'A catalyst is a substance that speeds up a chemical reaction but does not take part in the reaction.' Consider what a catalyst is understood to do, and evaluate whether the statement is technically correct.

Step 2: Correct Statement A

The correct version of the statement should clarify that a catalyst does take part in a reaction, but it is returned to its original form by the end of the reaction. Hence, the refined version reads: 'A catalyst is a substance that speeds up a chemical reaction by taking part in the reaction but is returned to its initial state by the end of the reaction.'

Step 3: Analyze Statement B

Next, analyze Statement B: 'The function of a catalyst is to lower the activation energy for a chemical reaction.' Consider whether a catalyst is indeed lowering the activation energy.

Step 4: Correct Statement B

The correct version of the statement should clarify that a catalyst doesn't directly lower the activation energy; instead, it provides an alternate reaction pathway that has a lower activation energy. The refined version reads: 'The function of a catalyst is to provide an alternate pathway for the chemical reaction that has a lower activation energy.'

Key Concepts

Chemical Reaction

A chemical reaction occurs when substances interact to form new products. These reactions involve breaking existing chemical bonds and forming new ones.

• Reactants are the starting substances that undergo change.
• Products are the new substances formed as a result of the reaction.
• The process is influenced by factors such as temperature, pressure, and concentration.

In a chemical reaction, reactants may be transformed into products through a series of steps, often involving intermediates. These steps collectively represent a reaction pathway, which connects the reactants to the products.

Activation Energy

Activation energy is the minimum amount of energy required for a reaction to proceed. It acts as a barrier that reactants need to overcome to transform into products.
This concept is crucial in determining how quickly a reaction will occur.

• Reactions with high activation energy tend to occur slowly, as fewer molecules have sufficient energy to overcome the barrier.
• Conversely, reactions with low activation energy happen more readily.

Catalysts are substances that alter the activation energy, thus influencing the rate of the reaction without altering the chemical structure of the reactants or products.

Reaction Pathway

The reaction pathway is a detailed map of the steps involved in converting reactants to products in a chemical reaction. This pathway can involve multiple steps, each with its own energy changes.

• Catalysts introduce an alternative reaction pathway. This pathway typically requires less energy, making the overall reaction easier and faster.
• By providing an alternative pathway, catalysts indirectly lower the activation energy of the reaction.
• They ensure that more reactive collisions have enough energy to overcome the activation barrier.

This alternative pathway is not a simple shortcut; it's a rearrangement of reaction steps that make the transformation of reactants to products more efficient.