7. Equilibrium

Question 1

Homogenous / Heterogenous reactions

Answer 1

• when all reactants and products are in one phase, the equilibrium is homogenous
• if one or more reactants or products are in a different phase, the equilibrium is heterogenous

Question 2

The Equilibrium Law

Answer 2

For an equilibrium reaction of the form

aA + bB <—> cC + dD

At constant temp:

[C]^c•[D]^d / [A]^a•[B]^b = Kc

• if Kc is very large, reaction goes to completion
• if Kc is very small, the reaction would be considered to not occur

Question 3

Le Chatelier’s Principle

Answer 3

Temperature

• the only thing that can change the value of Kc
• high temp moves equilibrium endothermic reaction right, exothermic reaction left

Concentration

• increased conc shifts equilibrium to the opposite side

Pressure

• increased pressure shifts to the side with the least moles

Question 4

Haber Process

Answer 4

N_2(g) + 3H_2(g) <—> 2NH_3(g)

_{dH = -92kJ/mol}

200 atm | 450 c | iron catalyst

• Equilibrium theory favors low temp, high pressure
• Kinetic theory favors high temp, pressure and catalyst
• conditions are a compromise with the catalyst so the reaction can happen at a lower temp

Question 5

Uses of Ammonia

Answer 5

• Fertilizers
• Nitric Acid
  
  • ammonia can be oxidised to nitric acid –> nitric acid can make fertilizers, explosives polyamide polymers

Question 6

The Reaction Quotent (Q)

Answer 6

aA + bB <—> cC + dD

Q = C^c x D^d / A^a x B^b

• used to determine if a reaction will occur
• used to determine if a salt will dissolve

Q > K products are great/ reverse reaction favored

Q = K both reactions occuring in equilibrium

Q < K reactants are great/ forward reaction favored

Question 7

Solubility Product Constant (Ksp)

Answer 7

For an insoluble salt:

MX_(s) <—> M⁺_(aq) + X^-_(aq)

The Keq will not change significantly

Ksp = [M][X]

Question 8

Gibbs Free Energy and the Equilibrium Constant

Answer 8

K = 1 Equilibrium dG = 0

K > 1 products favored dG < 1

K < 1 reactants favored dG > 1