Chemical Equilibrium: A Comprehensive Guide for Mechanical Engineering Students

Question 1

The equilibrium concentration of [H+] in a solution with a pH of 5 is:

Accepted Answer

1 x 10^-5 M

Answer

1 x 10^-7 M

Answer

1 x 10^-9 M

Answer

1 x 10^-11 M

Question 2

Which of the following is a characteristic of a weak acid?

Accepted Answer

Partially dissociates in water

Answer

Completely dissociates in water

Answer

Produces a high concentration of H+ ions in water

Answer

Produces a low concentration of H+ ions in water

Question 3

The conjugate base of NH4+ is:

Accepted Answer

NH3

Answer

NH2-

Answer

NH4OH

Answer

H2O

Question 4

Which reaction will have the highest Gibbs free energy change?

Accepted Answer

Reaction with a positive ΔG°

Answer

Reaction with a negative ΔG°

Answer

Reaction at equilibrium

Answer

Reaction with ΔG° = 0

Question 5

Which of the following reactions is an example of a homogeneous equilibrium?

Accepted Answer

Dissolving carbon dioxide in water

Answer

Reacting hydrogen with solid copper oxide

Answer

Combustion of propane gas

Answer

Electrolysis of water

Question 6

What is the relationship between the equilibrium constant and the standard free energy change (ΔG°) for a reaction?

Accepted Answer

K = e^(-ΔG°/RT)

Answer

K = ΔG°/RT

Answer

K = RT/ΔG°

Answer

K = -ΔG°/RT

Question 7

Which of the following factors does NOT affect the equilibrium position of a chemical reaction?

Accepted Answer

Magnetic field

Answer

Temperature

Answer

Pressure

Answer

Concentration

Question 8

What is the difference between a closed system and an open system in terms of chemical equilibrium?

Accepted Answer

Open systems can exchange matter with their surroundings, while closed systems cannot.

Answer

Closed systems reach equilibrium faster than open systems.

Answer

Closed systems have a fixed volume, while open systems do not.

Answer

Open systems are always at equilibrium, while closed systems are not.

Question 9

Which of the following equilibrium systems would be most sensitive to changes in temperature?

Accepted Answer

A reaction with a large positive ΔH°

Answer

A reaction with a small negative ΔH°

Answer

A reaction with a large equilibrium constant

Answer

A reaction with a small equilibrium constant

Question 10

What does the equilibrium constant (K) of a reaction represent?

Accepted Answer

The ratio of product concentrations to reactant concentrations at equilibrium.

Answer

The rate of the forward reaction relative to the reverse reaction.

Answer

The extent to which the reaction proceeds in the forward direction.

Answer

The activation energy required for the reaction to occur.

Question 11

In a titration experiment, a strong acid is titrated with a strong base. What is true about the pH at the equivalence point?

Accepted Answer

pH = 7 (neutral solution)

Answer

pH < 7 (acidic solution)

Answer

pH > 7 (basic solution)

Answer

pH cannot be determined without knowing the specific acid and base involved.

Question 12

Consider the equilibrium reaction: 2NO(g) + O2(g) <=> 2NO2(g) + heat. According to Le Chatelier's principle, what will happen to the equilibrium position if the temperature is decreased?

Accepted Answer

The equilibrium will shift towards the reactants (NO and O2).

Answer

The equilibrium will shift towards the products (NO2).

Answer

The equilibrium constant will change.

Question 13

If the volume of a closed system containing a gas-phase equilibrium reaction is decreased, which of the following is a possible outcome?

Accepted Answer

The equilibrium will shift towards the side with fewer moles of gas.

Answer

The equilibrium will not change.

Answer

The equilibrium will shift towards the side with more moles of gas.

Question 14

Consider the Haber process for the synthesis of ammonia: N2(g) + 3H2(g) <=> 2NH3(g) + heat. If additional hydrogen gas is added to the reaction mixture, how will the equilibrium position shift?

Accepted Answer

Towards the products (NH3).

Answer

Towards the reactants (N2 and H2).

Answer

The equilibrium will not change.

Answer

The reaction rate will increase.

Question 15

What is the value of the equilibrium constant for a reaction that has reached equilibrium?

Accepted Answer

Constant and independent of initial concentrations.

Answer

Infinity

Answer

Zero

Question 16

Which of the following statements about equilibrium is true?

Accepted Answer

Equilibrium is a dynamic process where the forward and reverse reactions occur at equal rates.

Answer

Equilibrium is a static state where no chemical change occurs.

Answer

Equilibrium is achieved when the concentrations of the reactants and products are equal.

Question 17

Consider the reaction: CO2(g) + H2(g) <=> CO(g) + H2O(g) at equilibrium. If the partial pressure of CO2 is increased, what will happen to the equilibrium position?

Accepted Answer

Shift towards the products (CO and H2O).

Answer

No change in equilibrium position.

Answer

Shift towards the reactants (CO2 and H2).

Question 18

Which of the following is a characteristic of a system at equilibrium?

Accepted Answer

The properties of the system do not change over time.

Answer

The system is constantly changing.

Answer

The forward reaction is occurring faster than the reverse reaction.

Question 19

What is the primary purpose of Le Chatelier's principle?

Accepted Answer

To predict the direction of equilibrium shift in response to changes in reaction conditions.

Answer

To calculate the equilibrium constant.

Answer

To explain the kinetics of chemical reactions.

Question 20

What is the equilibrium constant expression for the following gas-phase reaction: 2NO(g) + O2(g) <=> 2NO2(g)?

Accepted Answer

K = [NO2]^2 / ([NO]^2 * [O2])

Answer

K = [NO]^2 / ([NO2]^2 * [O2])

Answer

K = [NO2]^2 / ([NO] * [O2])

Answer

K = ([NO]^2 * [O2]) / [NO2]^2

Question 21

A solution of sodium acetate (CH3COONa) has a pH of 9.2. What is the approximate concentration of acetic acid (CH3COOH) in the solution? (Assume Ka for acetic acid is 1.8 x 10^-5)

Accepted Answer

0.01 M

Answer

0.1 M

Answer

1 M

Answer

10 M

Question 22

Which of the following factors does NOT directly affect the equilibrium constant (K) of a reaction?

Accepted Answer

Presence of a catalyst

Answer

Pressure (for gas-phase reactions)

Answer

Temperature

Answer

Concentration of reactants and products

Question 23

Which statement accurately describes chemical equilibrium?

Accepted Answer

Equilibrium is a dynamic state where the rates of the forward and reverse reactions are equal.

Answer

Equilibrium is only achievable in closed systems.

Answer

Equilibrium is a static state where the concentrations of reactants and products remain constant.

Question 24

Why does the solubility of a gas in a liquid decrease with increasing temperature?

Accepted Answer

The increased kinetic energy of the gas molecules causes them to escape from the liquid phase more easily.

Answer

The decreased pressure of the gas above the liquid is not the primary factor.

Answer

The decreased solubility of the gas in the liquid is the reason, not the consequence.

Answer

The formation of a gas-liquid interface is a consequence, not the cause.

Question 25

What is the common ion effect?

Accepted Answer

The decrease in the dissociation of a weak acid or base when a salt containing a common ion is added to its solution.

Answer

The increase in the solubility of a precipitate when a salt containing a common ion is added to its solution.

Question 26

In the acid-base reaction CH3COOH(aq) + H2O(l) <=> CH3COO-(aq) + H3O+(aq), which of the following actions will increase the pH of the solution?

Accepted Answer

Adding NaCH3COO

Answer

Adding H2O

Answer

Decreasing the temperature

Answer

Adding HCl