Chapter 6 Equilibirium

Question 1

Catalysts make reactions go … but they do not…

Answer 1

Catalysts make reactions go faster toward their equilibrium position but they do not change the equilibrium position or alter the value of K_eq

Question 2

Explain dynamic equilibrium.

Answer 2

In dynamic equilibrium, the forward and reverse reactions are still occurring (in static equilibrium, they stop), but they are going at the same rate. Thus, there is no change in the concentrations of the products or readtions.

Essentially, in dynamic equilibrium, the rate of the forward reaction = the rate of the reverse reaction

Question 3

What is entropy?

Answer 3

A measure of the distribution of energy throughout a system or between a system and its environment

Question 4

When will a reversible reaction reach equilibrium (where will the entropy and Gibbs free energy be)?

Answer 4

it will reach equilibrium when the system’s entropy (energy distribution) is at a maximum and the Gibbs free energy is at a minimum

Question 5

For a generic reversible reaction

aA + bB ⇌ cC + dD

what does the law of mass action state?

Answer 5

If the system is at equilibrium at a constant temperature, then the following ratio is constant:

Question 6

What is the ratio of the forward and reverse rate constant, k_f and k_r?

Answer 6

K_c = k_f/k_r

Question 7

What does the law of mass action define?

Answer 7

The law of mass action defines the position of equilibrium.

Question 8

What role does the reaction quotient, Q, serve?

Answer 8

It can be used to indicate how far the reaction has proceeded towards equilibrium. At any point during the reaction, the concentration of all reactants and products can be used, and the reaction quotient can be calculated.

Its value is compared to Keq to determine if the reaction proceeds forward or in reverse direction, or if it is at equilibrium.

Question 9

How do you calculate the reaction quotient?

Answer 9

Question 10

What does it mean when:

Q < K_eq

Q > K_eq

Q = K_eq

Answer 10

Q < K_eq → forward rxn has not reached equilibrium; greater concentration of reactants (small concentration of products); reaction proceeds in forward direction

Q > K_eq → forward rxn has exceeded equilibrium; greater concentration of products (small concentration of reactants); reaction proceeds in reverse direction

Q = K_eq → reactants and products are present in equilibrium proportions; forward and reverse rates of reaction are equal

Question 11

The larger the K_eq value …

Answer 11

The larger the K_eq value, the farther to the right the equilibrium position.

Question 12

If the equilibrium constant for a reaction written in one direction is K_eq, then the equilibrium constant for the reverse reaction is…

Answer 12

1/K_eq

Question 13

What does a large positive exponent for K_eq indicate?

Answer 13

A large exponent indicates that products are favored at equilibrium.

The larger the exponents, the less reactant that will be present at equilibrium.

A large positive exponent indicates a reaction goes almost to completion.

Question 14

What does a large negative exponent indicate?

Answer 14

A large negative exponent indicates a reaction that strongly favors reactants at equilibrium.

Only a small amount of reactant is converted to product.

Question 15

What type of exponent allows a shortcut to be made during equilibrium calculations, and wha is the shortcut?

Answer 15

A large NEGATIVE exponent allows for a shortcut. The amount that has reactant can be considered negligible compared to the amount of reactant that remains.

Question 16

What does Le Chatelier’s Principle state?

Answer 16

It states that if stress is applied to a system, the system shifts to relive that applied stress. The reaction is temporarily moved out of its equilibrium state.

Question 17

What happens when reactants are added (or products are removed) from a reaction in equilibrium?

Answer 17

If reactants are added (or products are removed), Q_c < K_eq, and the reaction will spontaneously react in the forward direction, increasing the value of Q_c until it equals K_eq.

Question 18

What happens if reactants are removed (products are added) to a reaction in equilibrium?

Answer 18

Q_c > K_eq

the reaction will spontaneously react in the reverse direction, decreasing the Q value until it equals the K value

Question 19

What needs to be present in a chemical reaction for the reaction to be impacted by a change in the system’s pressure and value?

Answer 19

At least one gaseous species needs to be present.

Question 20

What happens when a system in an equilibrium state is compressed?

Answer 20

When a system is compressed, the volume decreases and the total pressure increases.

The increase in total pressure is associated with an increase in the partial pressures of each gas in the system, and thus the system in no longer in an equilibrium state.

The system will move forward or in reverse, always towards whichever side has the lower total number of moles of gas. This is due to the ideal gas law, which states that there is a direct relationship between the number of moles of gas and the pressure of gas.

Question 21

What happens to a system in equilibrium when the volume of the system is expanded?

Answer 21

The total pressure and the partial pressures decrease when the volume increases. The system is no longer in equilibrium, and it will react in the direction of the side with the greater number of moles of gas in order to restore the pressure.

Question 22

How is the reactant quotient, Q_c or Q_p, impacted by a change in pressure?

Answer 22

Changing the temperature does not have an immediate impact on the reaction quotient. The change in temperature does not cause the concentrations or partial pressures of reactants and products to change immediately.

K_eq is impacted by changing the temperature.

Question 23

How does the system move at a new temperature trying to reach equilibrium (how is the direction determined)?

Answer 23

The direction is determined by the enthalpy of the reaction.

Question 24

When does heat function as a reactant, and when does it function as a product?

Answer 24

Heat functions as a reactant when the reaction is endothermic (delta H > 0).

Heat functions as a product when the reaction is exothermic (delta H <0).

Question 25

At lower temperatures, what type of product is formed?

Answer 25

At lower temperatures (with smaller heat transfer), a kinetic product is formed.

Question 26

At higher temperatures, what type of product is formed?

Answer 26

At higher temperatures (with a large heat transfer), a thermodynamic product is formed.