Ch 15 Chemical Equilibrium

Question 1

What is the protein the body uses to transport O2 via the blood? What are the reactants and products if this reverse reaction?

Answer 1

Hemoglobin is a protein (Hb) found in RBCs that reacts with O2.

Hb + O2 —>

Question 2

(T/F?) as a reaction starts, the reactants are consumed and product are made. As reactant concentration decreases, the forward reaction rate decreases as well.

Answer 2

True

Question 3

Processes that process in both the forward and reverse directions are said to be ______________?

Answer 3

Reversible

Question 4

(T/F) As the forward reaction slows and the reverse reaction accelerates, eventually they reach the same rate?

Answer 4

True

Question 5

Define Dynamic Equillibrium

Answer 5

The condition wherein the rates of the forward and reverse reactions are equal.

Once the reaction reaches equilibrium, the concentrations of all the chemical reactants remain constant because the chemicals are being consumed and made at the same time.

Question 6

What does it mean when someone says the equilibrium favors the products or the reactants?

Answer 6

Some reactions reach equilibrium after almost all the reactant molecules are consumed. In this instance, the concentrations favor the products.
Other reactions reach equilibrium after very little reactant is consumed. In this instance, the concentrations favor the products.

Question 7

Define the Law of Mass Action

Answer 7

Law of Mass Action - the relationship between the chemical equation and the concentration.

Question 8

What is the equation used to solve for the Law of Mass Action or Equilibrium Constant?

Answer 8

For the general equation:

aA + bB —>

Question 9

How does the value of Keq relate to 1, when the position of equilibrium favors the products? Give an example.

Answer 9

When the value of Keq&raquo_space;1, the Reaction reaches equilibrium when there will be many more product molecules than reactant molecules.

H2 + Br2 —>

Question 10

How does the value of Keq relate to 1, when the position of equilibrium favors the reactants? Give an example.

Answer 10

When the value of Keq «1, the Reaction reaches equilibrium when there will be many more reactant molecules than product molecules.

N2 + O2 —>

Question 11

Explain the relationships between the equilibrium constants and the following reactions:

1) aA + bB —>

Answer 11

1) Kforward = ([C]^c x [D]^d)/
([A]^a x [B]^b)

2) Kbackward = ([A]^a x [B]^b)/
([C]^c x [D]^d). Or

Kbackward = 1/Kforward

*When the reaction is written backward, the equilibrium constant is inverted.

Question 12

Explain the relationships between the equilibrium constants and the following reactions:

1) aA + bB —>

Answer 12

1) Koriginal = [C]^c/
([A]^a x [B]^b)

2) Knew = [C]^2c/
([A]^2a x [B]^2b

 Knew =        (Koriginal)^n

*When the coefficients of an equation are multiplied by a factor, the equilibrium constant is raised to that factor.

Question 13

Explain the relationships between the equilibrium constants and the following reactions:

1) aA —>

Answer 13

1) K1 = [B]^b/[A]^a
2) K2 = [C]^c/[B]^b
3) K3 = [C]^c/[A]^a or

 Knew = K1 x K2

• When you add equations to get a new equation, the equilibrium constant of the new equation is the product of the equilibrium constants of the old equations.

Question 14

Explain the relationships for the equilibrium constants for reactions involving gases.

Answer 14

1) The concentration of a gas in a mixture is proportional to its partial pressure.
2) Therefore, the equilibrium constant can be expressed as the ratio of the partial pressures of the gases.
3) For aA(g) + bB(g) —>

Question 15

(T/F) in calculating Kp, the partial pressures are always in atm.

Answer 15

True

Question 16

Why are the values of Kp and Kc not going always be equal?

Answer 16

Because Kp = Kc (RT)^🔺n

*Kp = Kc when 🔺n=0

Question 17

Explain 🔺n as it relates to Kp = Kc (RT)^🔺

Answer 17

🔺n is the difference between the coefficient of gaseous reactant and gaseous products.

🔺n = (c+d)-(a+b)

Question 18

What is the formula for the Ideal Gas Law?

Answer 18

Pv = NRT

N = # of moles
R = universal gas constant 8.3145 J/mol K

Question 19

Why are the concentrations of pure liquids and solids not included in the equilibrium constant expression?

Answer 19

Because the concentrations of pure liquids and solids do not change the course of a reaction.

Question 20

What is the most direct way of finding the equilibrium constant and why?

Answer 20

By measuring the amounts of reactants and products in a mixture at equilibrium.

The value of the equilibrium constant is independent of the initial amounts of reactants and products.

The equilibrium mixture may have different amounts of reactants and products, but the value of the equilibrium constant will always be the same, as long as the temperature is kept constant.

Question 21

If a reaction mixture containing both reactants and products is not at equilibrium, how can we determine from which direction the reaction will reach equilibrium?

Answer 21

By determining the reaction quotient.
Compare the current concentration ratios to the equilibrium constant.

The non-equilibrium concentration ratio of the products (raised to the power of their coefficients) to the reactants (raised to the power of their coefficients) is called the reaction quotient (Q).

Question 22

For the gas reaction:

aA + bB —>

Answer 22

Qc = ([C]^c * [D]^d) /
([A]^a * [B]^b)

Qp = (P^cC * P^dD)/
(P^aA * P^bB)

Question 23

How can you predict the direction of change of a reaction given the Reaction Quotient and the Equilibrium Constant?

Answer 23

1) Q > K: Reaction runs to the left
(A B)
3) Q = K: Reaction. Is at equilibrium
(A —>

Question 24

(T/F) if you have no product initially, the reaction will always run right (move forward).

Answer 24

True

Question 25

What are the 4 steps involved in finding equilibrium concentrations when given K and the initial concentrations or pressures?

Answer 25

STEP 1: Prepare the ICE table

STEP 2: Decide in which direction the reaction will proceed by comparing Q to K.

STEP 3: Define the changes of all substances in terms of x.

STEP 4: Solve for x. For 2nd order equations, take square roots of both sides or use the quadratic formula. Simplify and approximate the answer for very large or small equilibrium constants, if possible.

Question 26

What is the quadratic formula?

Answer 26

X = (-b +/- sqrt of b^2 - 4ac) / 2a

Question 27

Once a reaction is at equilibrium, the concentrations of all the reactants and products remain constant. However, what happens if the conditions are changed (aka, the equilibrium is disturbed)?

Answer 27

The concentrations of all the chemicals will change until equilibrium is restored.

The new concentrations will be different, but the equilibrium constant will be the same, unless there is a change in temperature.

Question 28

Explain Le Châtelier’s Principle

Answer 28

It states that if a system at equilibrium is disturbed, the position of equilibrium will shift to minimize the disturbance.

Disturbances include changing the concentration of a reactant or product, changing the volume or pressure, and changing the temperature.

Question 29

What happens when you disturb an equilibrium by adding reactants?

Answer 29

• As long as the added reactant is not a solid or a liquid:
  1) Adding a reactant increase the rate of the forward reaction. The reaction proceeds to the right until equilibrium is restored.
  2) At the new equilibrium position, you will have more of the products than before.
  3) At the new equilibrium position, the equilibrium constant is the same.

Question 30

What happens when you disturb an equilibrium by removing reactants?

Answer 30

• If the removed reactant is not a solid or a liquid:
  1) Removing a reactant initially decreases the rate of the forward reaction. The reaction proceeds to the left until equilibrium is restored.
  2) At the new equilibrium position, you will have less of the products than before.
  3) At the new equilibrium position, the equilibrium constant is the same.

Question 31

What are the effects on concentration when equilibrium is disturbed?

Answer 31

• Equilibrium shifts away from the side with added chemicals and toward the side with removed chemicals. Therefore:
  1) Adding a reactant will decrease the amounts of the other reactants and increase the amount of the products until a new position of equilibrium is found that has the same K.
  2) Removing a product will increase the amounts of the other products and decrease the amounts of the reactants. (You can use this to drive a reaction to completion).

Question 32

What happens when you disturb an equilibrium by changing the volume?

Answer 32

1) Decreasing container volume will increase total pressure, according to Boyle’s Law (PV=k).
2) When total pressure increases, the position of equilibrium will shift to decrease pressure (shifts toward the side with fewer gas molecules).
3) At the new equilibrium position, the equilibrium constant is the same.

Question 33

For the following reaction at equilibrium, what happens if the volume is decreased? Increased?

N2(g) + 3H2(g) —>

Answer 33

1) If volume is decreased then pressure is increased and the reaction will shift right towards the side of fewer gas molecules. (4 mols of gas on reactant side and 2 mols of gas on product side).
2) If volume is increases then pressure is decreased and the reaction will shift left towards the side of more gas molecules. (4 mols of gas on reactant side and 2 mols of gas on product side).

Question 34

What is the effect of adding a Gas to a Gas-Phase Reaction at Equilibrium?

Answer 34

1) Adding a gaseous reactant increases it’s partial pressure, causing the equilibrium to shift to the right.
2) Adding an inert gas (a noble gas) to the mixture, has no effect on the position of equilibrium. It does not affect the partial pressures of the gases in the reaction.

Question 35

What is the effect of temperature changes on a reaction at equilibrium?

Answer 35

1) for Endothermic reactions, heat is a reactant because you have to provide heat to move the reaction forward. Increasing the temperature is like adding heat ( a reactant) and will shift the reaction forward to produce more products.

2) For Exothermic reactions, heat is a product (heat is produced as a result of the reaction going forward).
Decreasing temperature is like removing a product and will shift the reaction forward to produce more heat.

Question 36

What are the effects of Catalysts on a reaction at equilibrium?

Answer 36

1) Catalysts provide an alternative, more efficient, mechanism.
2) Catalysts work for both forward and reverse reactions.
3) Catalysts affect the rate of the forward and reverse reactions by the same factor. Therefore, they do not affect the position of equilibrium.