Topics 10+11: Equilibrium I & II

Question 1

Equilibrium constant Kc

Answer 1

Measures position of equilibrium using concentration of reactants/products, where in:
nA + mB <-> pP + rR (n, m, p, r are stoichiometric ratios)
Kc = ([P]^p * [R]^r) / ([A]^n * [B]^m)
Concentration of products to the power of their coefficients divided by the conc. of reactants

[] refers to conc. of a species at equilibrium
All species included except solids
Kc is dependent on temperature, not initial pressure
Units are specific to each reaction & must be included in answer

Question 2

Dynamic equilibrium

Answer 2

Forward and back reaction occur simultaneously
At the same rate
[] of products and reactants remains constant
Kc = 1

(Smaller Kc, eq. shifts to the left)

Question 3

Equilibrium reactions

Answer 3

When reversible reactions occur in a closed system, both directions can happen at the same time
Initially only forward occurs
As products form, backwards start
As reaction goes on, rate of forward down and rate of backward up
Unit both rates are equal and equilibrium is dynamic

Question 4

Le Chatelier’s Principle

Answer 4

Reversible reactions respond to oppose changes in [], temp and pressure
1) when conc. of one side increases, other side is favoured
2) when temperature increases, endothermic direction is favoured (to lower it)
3) when pressure increases, side with less moles of gas (or liquid) is favoured

Question 5

Kp Constant

Answer 5

In a closed system, each species exerts a partial pressure that contributes to the total
Kp = (pProducts)^x / (pReactants)^y
where p is partial pressure and x and y are the stoichiometric ratios of the species

Question 6

Mole fractions

Answer 6

Mole fraction is proportional to the partial pressure
mole f = moles of gas / total moles of gas in mix (both reactants & products)
partial pressure = mole fraction x total pressure