Quiz 9: Equilibrium Concepts and Calculations in Chemistry

Reverse reaction rate

At equilibrium, _____________________ = forward reaction rate

H2O(g) + CO(g) ⇄ H2(g) + CO2(g)

and

H2(g) + CO2(g) ⇄ H2O(g) + CO(g)

What 2 reactions are occurring in the reaction below?

H2O(g) + CO(g) ⇄ H2(g) + CO2(g)

Stay constant

At equilibrium, concentration of all components of reaction will ______________

True

True or False:

All reactions will reach equilibrium if given enough time

False, they still reach equilibrium, but the concentration of reactants is very small

True or False:

Non-equilibrium reactions that use normal reaction arrows (→) do not reach equilibrium

Equilibrium

When both reactions occur at the same time, this is referred to as _______________

Kc = [Products]^coefficient / [Reactants]^coefficient

What equation is used to solve for the Equilibrium Constant (KC)?

Homogenous equilibrium

The reactants and products of a reaction in __________________ are all in the same state of matter (g) (aq)

Heterogenous equilibrium

The reactants and products of a reaction in __________________ have different states of matter

True

True or False:

K is temperature-dependent

True

True or False:

We can calculate Kc if we know the concentrations equilibrium

Kc = [H2] [CO2] / [H2O] [CO]

(0.0166)(0.0166)/ (0.0034)(0.0034) = 24

Solve for Kc:

H2O(g) + CO(g) ⇄ H2(g) + CO2(g)

H2 M = 0.0166

CO2 M = 0.0166

H2O M = 0.0034

CO M = 0.0034

Kp - uses pressure values

Kc - uses molarity (mol/L)

To solve for the equilibrium constant for gases (Kp) _____________ are used in contrast to _____________ being used to solve for Kc

Kp = [P(CO)] x [P(H2)]^3 / [P(CH4)] [P(H2O)]

(0.0541)(0.162)^3/ (2.34)(2.34) = 4.20 x 10^-5

Solve for the equilibrium constant for gases (Kp):

CH4(g) + H2O(g) ⇄ CO(g) + 3H2(g)

P(CH4) = 2.34 atm

P(H2O) = 2.32 atm

P(CO) = 0.0541 atm

P(H2) = 0.162 atm

Kp = Kc (RT)^ng

What is another equation used to solve for Kp

ng = gaseous product mol - gaseous reactant mol

What equation is used to solve for ng in Kp = Kc (RT)^ng

ng = 2 - (1+3) = -2

KP = (6.0 x 10^-2)(0.08206 x 773)^-2 = 1.5 x 10^-5

N2(g) + 3H2(g) ⇄ 2NH3(g)

If Kc = 6.0 x 10^-2 at 500 degrees celsius, what is the value of Kp?

False, Kp = Kc when ng = 0

True or False:

Kp can never equal Kc

PCl5(g) ⇄ PCl3(g) + Cl2(g)

Kc = [PCl3] [Cl2] / [PCl5] = 1/25 = 0.040

Manipulating Equilibrium laws:

PCl3(g) + Cl2(g) ⇄ PCl5(g)

If Kc = 25, what is the value of Kc when the reaction is reversed?

2PCl3(g) + 2Cl2(g) ⇄ 2PCl5(g)

Kc = [PCl5]2 / [PCl3]2[Cl2]2 = 25^2 = 625

Manipulating Equilibrium laws:

PCl3(g) + Cl2(g) ⇄ PCl5(g)

If Kc = 25, what is the value of Kc when the reaction is multiplied by 2?

1. Rewrite reactions if needed

no need

2. Add reactions

2N2(g) + 4O2(g) ⇄ 4NO2(g)

3. Multiple values of K

Kc = (1.4 x 10^-3)(2.2 x 10^2) = 3.1 x 10^-1

4. Multiple by ½ to match the original reaction

½ x [2N2(g) + 4O2(g) ⇄ 4NO2(g)]

N2(g) + 2O2(g) ⇄ 2NO2(g)

5. Solve for Kc

Kc = (3.1 x 10^-1)^1/2 = 0.56

Manipulating Equilibrium laws: Solve for Kc:

N2(g) + 2O2(g) ⇄ 2NO2(g)

Given →

2N2(g) + O2(g) ⇄ 2N2O(g)

K1 = 1.4 x 10^-3

2N2O(g) + 3O2(g) ⇄ 4NO2(g)

K2 = 2.2 x 10^2

1. Rewrite reactions if needed

2C ⇄ A + B K1 = 1/24 = 0.042

4D + 2F ⇄ 2C K2 = (0.016)2 = 2.56 x 10-4

2. Add reactions

4D + 2F ⇄ A + B

3. multiple values of K to solve for Kc

Kc = (0.042)(2.56 x 10^-4) = 1.1 x 10^-5

Manipulating Equilibrium laws: Solve for Kc:

4D + 2F ⇄ A + B

Given →

A + B ⇄ 2C K1 = 24

2D + F ⇄ C K2 = 0.016

1. Rewrite reactions if needed

2CO(g) + O2(g) ⇄ 2CO2(g) K1 = 3.3 x 10^91

2H2O(g) ⇄ 2H2(g) + O2(g) K2 = 1 / (9.1 x 10^80)

2. Add reactions

2CO(g) + 2H2O(g) ⇄ 2CO2(g) + 2H2(g)

3. Multiply values of K

(3.3 x 10^91)(1/9.1 x 10^80) = 3.6 x 10^10

4. Multiple by 1/2 to match original reaction

½(2CO(g) + 2H2O(g) ⇄ 2CO2(g) + 2H2(g))

CO(g) + H2O(g) ⇄ CO2(g) + H2(g)

5. Solve for Kc

Kc = (3.6 x 10^10)1/2 = 1.9 x 10^5

Manipulating Equilibrium laws: Solve for Kc:

H2O(g) + CO(g) ⇄ CO2(g) + H2(g)

Given →

2CO(g) + O2(g) ⇄ 2CO2(g)

K1 = 3.3 x 10^91

2H2(g) + O2(g) ⇄ 2H2O(g)

K2 = 9.1 x 10^80

[Products] > [Reactants]

Product - favored

Equilibrium Constant (K):

If K > 1 , [ ___________ ] > [ _____________ ] which means the reaction is ______________- favored

[Products] < [Reactants]

Reactant- favored

Equilibrium Constant (K):

If K < 1 , [ ___________ ] < [ _____________ ] which means the reaction is ______________- favored

[Products] = [Reactants]

In between product-favored and reactant-favored

Equilibrium Constant (K):

If K = 1 , [ ___________ ] = [ _____________ ] which means the reaction is ______________

If K >> 1 → complete reaction

Equilibrium Constant (K):

If K >> 1 this indicates that there is a ____________ reaction

If K << 1 → no reaction

Equilibrium Constant (K):

If K << 1 this indicates that there is _______________ reaction

(→)

The __________ in a reaction indicates that the reaction goes to completion

Reaction Quotient (Q)

The _____________ can be calculated while not at equilibrium

at equilibrium

Reaction Quotient (Q):

If Q = K, the reaction is _______________

Q < K - shifts to products

Q > K - shifts to reactants

Reaction Quotient (Q):

If Q < K, the reaction shifts to _____________ to reach equilibrium

If Q > K, the reaction shifts to ______________ to reach equilibrium

shifts to products - too many reactants

shifts to reactants - too many products

Reaction Quotient (Q):

A reaction shifts to products to reach equilibrium when there are too many ____________ (Q < K)

A reaction shifts to reactants to reach equilibrium when there are too many _____________ (Q > K)

Qc = [NO]^2/ [N2][O2]

(0.0067)^2 / (0.50)(0.25) = 0.00036

Solve for Qc:

At 2300K, Kc = 0.0015

N2(g) + O2(g) ⇄ 2NO(g)

[N2] = 0.50M

[O2] = 0.25M

[NO] = 0.0067M

Q < K

shifts to the Right (products)

If Kc = 0.0015 and Qc = 0.00036

what direction does the reaction need to shift to in order to reach equilibrium?

- solids

- liquids

______________ and _____________ are not included in the equilibrium Law for Heterogeneous equilibrium reactions

solids not included

Kc = 1/ [SO2]

Heterogenous equilibrium: Solve for Kc:

CaO(s) + SO2(g) ⇄ CaSO3(s)

solids not included

Kc = [H2O][CO2]

Heterogenous equilibrium: Solve for Kc:

2NaHCO3(s) ⇄ Na2CO3(s) + H2O(g) + CO2(g)