Chapter 18, Problem 79E

Interpretation Introduction

(a)

Interpretation:

The difference between a reaction and a reversible reaction is to be stated.

Concept introduction:

In a chemical reaction, reactants react to produce products. The reactants are written on the left hand side of a reaction and the products are written on the right hand side of the reaction.

Answer to Problem 79E

The difference between a reaction and a reversible reaction is that combination of two or more substances or decomposition of a substance to form new substances is known as a chemical reaction whereas a reaction that proceeds in both the forward and the backward directions is known as a reversible reaction.

Explanation of Solution

When a substance reacts with another substance, gas or undergoes decomposition to produce new substances, then it is said that a chemical reaction has taken place. The reactants undergo reaction to produce products. In a chemical equation, the reactants are written on the left hand side and the products are written on the right hand side. For example, in the reaction ${\text{PCl}}_{\text{3}}\left(\text{g}\right)+{\text{Cl}}_{\text{2}}\left(\text{g}\right)\rightleftharpoons {\text{PCl}}_{\text{5}}\left(\text{g}\right)$, the reactants ${\text{PCl}}_{\text{3}}$ and ${\text{Cl}}_{\text{2}}$ react with each other to form ${\text{PCl}}_{\text{5}}$ as the product.

A reaction that proceeds in both the directions, that is, the reactants react to form products and the products react to give back the reactants is known as a reversible reaction. For example, in the reaction ${\text{H}}_2\left(\text{g}\right)+{\text{I}}_{\text{2}}\left(\text{g}\right)\rightleftarrows \text{2HI}\left(\text{g}\right)$, the reactants ${\text{H}}_2$ and ${\text{I}}_{\text{2}}$ react to form $\text{HI}$ as the product and $\text{HI}$ can decompose to form ${\text{H}}_2$ and ${\text{I}}_{\text{2}}$.

Conclusion

The combination of two or more substances or decomposition of a substance to form new substances is known as a chemical reaction whereas a reaction that proceeds in both the forward and the backward directions is known as a reversible reaction.

Interpretation Introduction

(b)

Interpretation:

The difference between an open system and a closed system is to be stated.

Concept introduction:

A reaction is said to be in equilibrium if the rate at which the forward reaction takes place becomes equal to the rate at which the backward reaction takes place. If any of the factors that affect the equilibrium changes, then the reaction shifts in either forward or backward direction so that the equilibrium condition is reestablished.

Answer to Problem 79E

The difference between an open system and a closed system is that matter and energy can be exchanged with the surroundings in an open system, whereas, only energy can be exchanged with the surroundings in a closed system.

Explanation of Solution

The system is the region in the universe that is under consideration. The rest of the universe excluding the system is known as the surroundings. The system in which exchange of matter and energy with the surroundings takes place is known as an open system. The system in which only exchange of energy with the surroundings takes place is known as a closed system. Exchange of matter does not take place in a closed system.

Conclusion

In an open system, matter and energy can be exchanged with the surroundings, whereas, in a closed system, only energy can be exchanged with the surroundings.

Interpretation Introduction

(c)

Interpretation:

The difference between dynamic equilibrium and static equilibrium is to be stated.

Concept introduction:

A reaction is said to be in equilibrium if the rate at which the forward reaction takes place becomes equal to the rate at which the backward reaction takes place. If any of the factors that affect the equilibrium changes, then the reaction shifts in either forward or backward direction so that the equilibrium condition is reestablished.

Answer to Problem 79E

The difference between dynamic equilibrium and static equilibrium is that both the forward reaction and the reverse reaction take place simultaneously in dynamic equilibrium, whereas the reactants and the products are in a state of rest in static equilibrium.

Explanation of Solution

In a dynamic equilibrium, both the forward reaction and the reverse reaction are taking place at the same rate. It means that even though the reaction is at equilibrium, both the processes are taking place simultaneously. In a static equilibrium, the amount of reactants and the amount of products remain the same but the reaction has stopped. This means that reactants are not changing into products and the products are not changing back into the reactants.

Conclusion

In dynamic equilibrium, both the forward reaction and the reverse reaction take place simultaneously, whereas in static equilibrium, the reactants and the products are in a state of rest.

Interpretation Introduction

(d)

Interpretation:

The difference between transition state and activation energy is to be stated.

Concept introduction:

According to collision theory, reactant molecules collide with proper orientation and sufficient energy to form products. Activation energy can be defined as the amount of energy that is required to convert reactant molecules into products.

Answer to Problem 79E

The difference between transition state and activation energy is that the transition state is the point at which the energy of the reaction is the maximum, whereas, the activation energy is the energy required by the reactant molecules to form the transition state.

Explanation of Solution

In a chemical reaction, the transition state is the point at which the energy of the reaction is the maximum. The reactant molecules need to cross the transition state in order to form products. The activation energy is the energy required by the reactant molecules, other than the energy possessed by them, to form the transition state that decomposes to form products.

Conclusion

The point at which the energy of the reaction is the maximum is known as the transition state, whereas, the energy required by the reactant molecules to form the transition state is known as the activation energy.

Interpretation Introduction

(e)

Interpretation:

The difference between catalyzed reaction and uncatalyzed reaction is to be stated.

Concept introduction:

A reaction is said to be in equilibrium if the rate at which the forward reaction takes place becomes equal to the rate at which the backward reaction takes place. If any of the factors that affect the equilibrium changes, then the reaction shifts in either forward or backward direction so that the equilibrium condition is reestablished.

Answer to Problem 79E

The difference between catalyzed reaction and uncatalyzed reaction is that catalyzed reaction takes place in the presence of a catalyst, whereas, an uncatalyzed reaction takes place in the absence of a catalyst.

Explanation of Solution

A catalyzed reaction is a reaction that takes place in the presence of a catalyst. A catalyst is a substance that does not get consumed in the reaction but it participates by lowering the activation energy of the reaction. A catalyst creates a new reaction pathway, having lower activation energy. Due to this, more amounts of reactants collide to form products, thereby attaining the equilibrium of the reaction at a faster rate. An uncatalyzed reaction is a reaction that takes place in the absence of a catalyst.

Conclusion

The reaction that takes place in the presence of a catalyst is known as a catalyzed reaction, whereas, a reaction that takes place in the absence of a catalyst is known as an uncatalyzed reaction.

Interpretation Introduction

(f)

Interpretation:

The difference between a catalyst and an inhibitor is to be stated.

Concept introduction:

A reaction is said to be in equilibrium if the rate at which the forward reaction takes place becomes equal to the rate at which the backward reaction takes place. If any of the factors that affect the equilibrium changes, then the reaction shifts in either forward or backward direction so that the equilibrium condition is reestablished.

Answer to Problem 79E

The difference between a catalyst and an inhibitor is that catalyst is a substance that increases the rate at which the reaction is taking place, whereas, inhibitor is a substance that decreases the rate at which the reaction is taking place.

Explanation of Solution

A catalyst is a substance that does not get consumed in the reaction but it participates by lowering the activation energy of the reaction. A catalyst helps to increase the rate of the chemical reaction. An inhibitor is a substance that decreases the rate at which the reaction is taking place.

Conclusion

A catalyst increases the rate at which the reaction is taking place, whereas, an inhibitor decreases the rate at which the reaction is taking place.

Interpretation Introduction

(g)

Interpretation:

The difference between a buffered solution and an unbuffered solution is to be stated.

Concept introduction:

The acids that do not undergo complete dissociation when dissolved in water are known as weak acids. The equilibrium constant in the case of dissociation of a weak acid is known as the acid constant and is denoted by ${\text{K}}_{\text{a}}$. A solution that resists any change in the value of pH when a very small amount of base or an acid is added to it is known as a buffer solution.

Answer to Problem 79E

The difference between a buffered solution and an unbuffered solution is that the value of pH does not change when a little amount of acid or base is added to a buffered solution, whereas, the value of pH changes on addition of acid or a base to an unbuffered solution.

Explanation of Solution

In a buffered solution, any change in the value of pH, when a very small amount of base or an acid is added to it, does not take place. The excess acid or base added to the solution is neutralized by the buffer. In an unbuffered solution, the value of pH changes rapidly on addition of an acid or a base.

Conclusion

In a buffered solution, the value of pH does not change when a little amount of acid or base is added to it, whereas, in an unbuffered solution, the value of pH changes on addition of acid or a base to it.