Chapter 3: 3.1 The Equilibrium Constant

Question 1

Define:

Equilibrium

Answer 1

The condition where the rate of forward reaction equals rate of reverse reaction

Question 2

What is the symbol used for equilibrium constant?

Answer 2

K

Question 3

True or False:

Equilibrium constants are temperature dependent

Answer 3

True

Question 4

Define:

Homogeneous equilibrium

Answer 4

If all the components are in the same phase in a system

Question 5

Define:

Heterogeneous equilibrium

Answer 5

If the components are in different phases in a system

Question 6

Are solids included in the equilibrium constant expression?

Answer 6

No

Question 8

How is the general equilibrium reaction written?

Answer 8

aA + bB ⇌ cC + dD
* A and B are reactants
* C and D are products

Question 9

State:

The general form of the equilibrium constant expression for this reaction, using concentrations

Answer 9

K = [C]^c[D]^d/[A]^a[B]^b

Question 10

True or False:

K is unitless

Answer 10

True, K is unitless and based on activities

Question 11

List:

Subscripts and meanings for K

Answer 11

• (aq) = Concentration (M or mol/L)
• (g) = Partial Pressure (bar or atm)
• (sp) = Solubility

Question 12

How is the proper thermodynamic definition of the equilibrium constant given?

Answer 12

Given in terms of properties called:
* Activity: For species in a solution
* Fugacity: For gas-phase species

Question 13

What are activity and fugacity related to?

Answer 13

Concentration and partial pressure

Question 14

True or False:

Activity and fugacity have units

Answer 14

False, they are dimensionless

Question 15

What should be the only unit used in calculations of K?

Answer 15

M

Question 16

State the significance of the magnitude of K when:

1. K is greater than 1
2. K is less than 1

Answer 16

1. Equilibrium lies toward the right (product side) of the equation, indicating more products than reactants
2. Equilibrium lies toward the left (reactant side) of the equation, indicating more reactants than products

Question 17

State the new K value when:

Reversing an Equilibrium Reaction

Answer 17

1/K (original)

Question 18

State the new K value when:

Multiplying/Dividing an Equilibrium Reaction

Answer 18

When multiplied by some coefficient, m, the new K value is K^m

Question 19

State the new K value when:

Combining Equilibria

Answer 19

K (new) = K (1) * K (2)

Question 20

How is K and Amounts determined?

Answer 20

1. K: Can be found is equilibrium amounts of each species involved are known
2. Amounts: Can be found if K is known via stoichiometry

Question 21

Defineand state the notation for:

Reaction quotient

Answer 21

The number that indicates whether the system is at equilibrium, and the direction in which the reaction must proceed to attain equilibrium
* Q

Question 22

What must be known in order for reaction quotient to be calculated?

Answer 22

Amounts of products and reactants

Question 23

The expression for Q is the same as K except for what?

Answer 23

The concentrations used are not necessarily equilibrium concentrations

Question 24

In terms of Q and K:

When is a system at equilibrium?

Answer 24

When Q=K

Question 25

If Q > K...

Answer 25

* System not at equilibrium * Must proceed in reverse direction * Too much product OR not enough reactant

Question 26

If Q < K...

Answer 26

* System not at equilibrium * Must proceed in forward direction * Too much reactant OR not enough product

Question 27

# Define: Le Châtelier's Principle

Answer 27

If a chemical system at equilibrium is disturbed by a change in temperature, pressure, or the concentration of a participant in the equilibrium, the equilibrium will shift in such a way as to minimize the disturbance

Question 28

# Applying Le Châtelier's Principle: How does concentration/partial pressure change by addition or removal of a species change the equilibrium?

Answer 28

1. If reactants are removed, then Q will be smaller than K, meaning the reaction will proceed forward until Q = K again 2. If products are removed, then Q will be larger than K, meaning the reaction will proceed backwards until Q = K again

Question 29

# Applying Le Châtelier's Principle: Total Pressure Change by a Volume Change

Answer 29

Example: 4 moles of reactants, 2 moles of products 1. If volume is increased the reaction will proceed backwards until equilibrium is reached 2. If volume is decreased the reaction will proceed forwards until equilibrium is reached

Question 30

# True or False: Le Châtelier's Principle applies to systems with solids and liquids when volume changes

Answer 30

Depends. If the system is JUST solids and liquids, changing the volume will not affect anything

Question 31

# True or False: If the moles of reactants and products are the same in a gaseous system, changing the volume will not affect the system (according to Le Châtelier's Principle)

Answer 31

True

Question 32

# Applying Le Châtelier's Principle: Relationship Between Temperature and K Values

Answer 32

***For an exothermic reaction***, heat is released thus is a product 1. Increasing the temperature = Increasing amount of products, thus the K value will decrease as the equilibrium will be shifted to the left ***For an endothermic reaction***, heat is required thus is a reactant 1. Increasing the temperature = Increasing amount of reactants, thus the K value will increase as the equilibrium will be shifted to the right

Question 33

# Applying Le Châtelier's Principle: Gibbs Free Energy and the Equilibrium Constant

Answer 33

1. If ΔG^o is positive, the equilibrium lies to the left (reactant) side and K is small 2. If ΔG^o is negative, the equilibrium lies to the right (product) side and K is large

Question 34

# True or False: A positive ΔG^o means the process is nonspontaneous under standard conditions, which means that it does not proceed at all

Answer 34

False, this means that it only proceeds to a very small extent

Question 35

# List The process and relationship between ΔG^o and K

Answer 35

1. ΔG = ΔG^o + RTlnQ 2. As ΔG = 0 and Q = K at equilibrium: ΔG^o = -RTlnK

Question 36

# In the formula ΔG^o = -RTlnK: State what each variable is

Answer 36

* ΔG^o is standard Gibbs free energy for the reaction in J/mol (standard conditions means 25 degrees Celsius, 1 atm pressure, and 1M concentration for everything in solution) * R is gas constant (8.314 J/mol K) * T = 298.15 K (standard conditions) * K is equilibrium constant

Question 37

# State the formula for: Standard free energy change using enthalpy and entropy changes

Answer 37

ΔG^o = ΔH^o - TΔS^o

Question 38

# True or False: While standard free energy change varies over temperature, standard enthalpy and entropy change varies little over temperature

Answer 38

True

Question 39

# State the formula for: Finding K values at temperatures other than standard (298.15 K)

Answer 39

lnK = -ΔH^o/RT + ΔS^o/R | (Substituting ΔG^o for -RTlnk and dividing by -RT)

Question 40

# State the formula and purpose of: van't Hoff Equation

Answer 40

ln K2/K1 = ΔH^o/R (1/T1 - 1/T2) * Used to determine K at a second temperature (T2), given ΔH^o rxn, K1 and T1

Question 41

What are alternative uses for van't Hoff equation?

Answer 41

1. If K is known at two different temperatures, the equation may also be used to calculate ΔH^o rxn 2. Determining the appropriate temperature at which to carry out a reaction