Question

In a reversible reaction, the catalyst: (a) Decreases activation energy of forward reaction (b) Increases activation energy of forward reaction (c) Decreases activation energy of both forward and backward reactions (d) Increases activation energy of backward reaction

Short answer

(c) Decreases activation energy of both forward and backward reactions.

Step-by-step solution

Understanding the Role of a Catalyst

A catalyst in a chemical reaction is a substance that increases the rate of a reaction without itself undergoing any permanent chemical change. It's important to remember that a catalyst works by decreasing the activation energy needed for the reaction to proceed.

Effect on Forward and Backward Reactions

In a reversible reaction, the presence of a catalyst affects both the forward and backward reactions. Since the catalyst lowers the activation energy for both directions of the reaction, it equally facilitates these processes without affecting the equilibrium position.

Identifying the Correct Answer

Given the options, we are looking for which statement correctly describes the role of the catalyst in a reversible reaction. - Option (a) is not fully correct because it only mentions the forward reaction. - Option (b) and (d) are incorrect as catalysts do not increase activation energies. - Option (c) correctly states that a catalyst decreases the activation energy for both the forward and backward reactions.

Key concepts

Activation Energy

Activation energy is the minimum amount of energy that reactants need to start a chemical reaction. It's like a hurdle that molecules must overcome in order for a reaction to occur. The activation energy determines the rate of a reaction: higher activation energy means a slower reaction, while lower activation energy allows the reaction to proceed more quickly.

• In a chemical graph, the activation energy appears as a peak that reactants need to climb before turning into products.
• This energy peak must be overcome for molecules to rearrange and form different substances.

Catalysts are amazing because they lower this energy barrier, making it easier for chemical reactions to happen. This doesn't mean the catalyst changes the direction or the final products of the reaction. Instead, it just provides an easier path for the reaction to proceed, like giving you a bicycle to race up a steep hill instead of having to walk. It's important to note that the catalyst doesn't get consumed in the reaction. It remains unchanged and can be used repeatedly.

Chemical Equilibrium

Chemical equilibrium is like a peaceful balance in a reversible reaction where the rate of the forward reaction equals the rate of the backward reaction. Imagine it like a game of tug-of-war where both sides have equal strength, and the rope stays centered.
At equilibrium, the concentrations of reactants and products remain constant over time, not because things stop moving, but because they move at an equal rate.

• The equilibrium state doesn't mean the amounts of reactants and products are equal, just that they no longer change.
• A catalyst can speed up how quickly equilibrium is reached, but it does not affect the concentration of reactants and products at equilibrium.

Equilibrium plays a key role in chemical reactions, especially in industrial processes, where reaching equilibrium quickly can save time and resources. When a catalyst is introduced, it accelerates both the forward and the backward reactions equally, maintaining the equilibrium position but allowing the system to reach that state faster.

Reaction Rate

The reaction rate tells us how fast or slow a chemical reaction happens. Think of it like the speedometer in a car measuring how quickly you reach your destination. Reaction rates can be influenced by several factors:

• Concentration of reactants: Higher concentrations usually increase the reaction rate.
• Temperature: Higher temperatures provide energy to the molecules, making them collide more frequently and energetically.
• Presence of a catalyst: Catalysts lower the activation energy barrier, speeding up the reaction.

When a catalyst is added to a reaction, it speeds up both the forward and backward reactions without altering the underlying chemical equilibrium. Imagine you and a friend racing towards an endpoint with hurdles (representing activation energy). A catalyst acts like a boost that reduces the height of each hurdle, enabling both of you to run faster.
While catalysts help in achieving a desired reaction rate, they do not alter the proportions of reactants and products in a chemical reaction. They ensure the reaction happens faster but do not change the final mix at equilibrium.