Question

Which of the following explains the increase of the reaction rate by catalyst: (a) Catalyst decreases the rate of backward reaction so that the rate of forward reaction increases (b) Catalyst provides extra energy to reacting molecules so that they may reduce effective collisions (c) Catalyst provides an alternative path of lower activation energy to the reactants (d) Catalyst increases the number of collisions between the reacting molecules.

Short answer

Option (c), because a catalyst provides an alternative reaction pathway with a lower activation energy, increasing the reaction rate.

Step-by-step solution

Understanding Reaction Rate and Catalysts

Reaction rate refers to the speed at which reactants are converted into products in a chemical reaction. A catalyst is a substance that increases the rate of a chemical reaction without itself being consumed. It works by providing an alternative pathway for the reaction with a lower activation energy.

Analyzing the Options

Option (a) is incorrect because a catalyst does not discriminate between the forward and backward reactions; it accelerates both, maintaining the equilibrium constant. Option (b) is also incorrect because a catalyst does not provide extra energy to the molecules. Instead, it lowers the energy barrier to reaction. Option (d) is incorrect as well, as a catalyst does not directly affect the number of collisions, but rather it affects the energy required for the collisions to be effective. Option (c) is the correct answer as it correctly describes the action of a catalyst - it provides an alternative pathway with lower activation energy for the reaction, which increases the reaction rate.

Selecting the Correct Answer

After considering the role of a catalyst in chemical reactions, we can determine that the correct explanation is given by option (c).

Key concepts

Chemical Reaction Kinetics

When we delve into the intricacies of chemical reactions, one aspect that always demands attention is the reaction kinetics, which is the study of rates of chemical processes. Simple, isn't it? Imagine a race between molecules to become products; reaction kinetics is the commentary telling us how fast they're moving. It tells us the 'rate' at which the reactants are transformed into products.

This rate can be influenced by various factors, such as the concentration of the reactants, the temperature of the system, the presence of a catalyst, and the physical state of the reactants. A catalyst, our superhero in the realm of chemical reactions, steps in and says, 'Let me help you with that!' It makes the reaction go faster without being used up in the process. How it does this is a fantastic bit of chemistry magic that ties into our next topic – activation energy.

Activation Energy

Picture activation energy as the height of a hill that reactants must climb over to react and turn into products. It's like the energy hump they need to get over before they can slide down into the valley of stability. We call this 'hill' the activation energy, and it's what keeps molecules from spontaneously transforming into new substances.

However, what if there were a shortcut? Imagine a tunnel through the hill that's not as steep as the hill itself. Here's where a catalyst comes into play; it effectively makes a tunnel through the hill, lowering the 'activation energy'. Instead of having to climb all the way to the top, reactants can use the catalyst's path, requiring less energy. By lowering the activation energy, the rate at which the reactants are converted into products – also known as the reaction rate – is increased, meaning a faster reaction.

Equilibrium Constant

Now, let's chat about the equilibrium constant, often symbolized as K_eq. This is like the scorecard that tells us the balance of a chemical reaction. When a reaction reaches a point where the rate of the forward reaction equals the rate of the reverse reaction, it's said to be in a state of dynamic equilibrium. At this point, the concentrations of reactants and products remain constant over time, as they are formed and used up at the same rate.

The equilibrium constant is a number that gives us the ratio of the concentration of the products to the concentration of the reactants. Each reaction has its unique K_eq, which is determined by the nature of the reactants and products as well as the temperature. Amazingly, the presence of a catalyst doesn't change the equilibrium constant; it simply gets the reaction to equilibrium faster. So, for our enthusiastic students, always remember that while the catalyst is changing the rate of the reaction, it's not tilting the balance – it's accelerating both the forward and backward reactions equally, keeping the equilibrium constant, constant.