5B - Equilibria definitions

Question 1

Dynamic equilibrium

Answer 1

The equilibrium that exists in:

• A closed system
• When the rate of the forward reaction = rate of backward reaction
• Concentration (or anything macrophysical - can be measured) don’t change
• The equilibrium can be approached from both sides

Question 2

Equilibrium law = ?

Answer 2

aA + bB ⇌ cC + dD

Question 3

Equilibrium law and Kc relationship = ?

Units?

Answer 3

Kc units will vary but each of the concenrations = moldm^-3

Question 4

Homogeneous equilibrium

Answer 4

An equilibrium in which all the species making up the reactants and products have the same physical state

Question 5

Heterogeneous equilibrium

Answer 5

An equilibrium in which the species making up the reactants and products have different physical states

Question 6

Ideal gas law = ?

Units = ?

Answer 6

PV = nRT

P = Pressure / Pa

V = Volume / m³ (1m³ = 1000dm³ = 1 x 10⁶cm³)

n = Moles

R = Gas constant (on data sheet)

T = Temperature / K (+273 to convert from °C → K)

Question 7

Mole fraction = ?

Answer 7

Mole fraction of gas A = Moles of gas A / Total moles of gas in the mixture

Question 8

Partial pressure of gas A = ?

Answer 8

Partial pressure of gas A = Mole fraction x Total pressure

Mole fraction of gas A = Moles of gas A / Total no’ of moles in mixture

Question 9

Kp = ?

Units = ?

Answer 9

Question 10

Total pressure = ?

Answer 10

P_Total = n_Total x (RT / V)

(rearrangement of PV = nRT)

You could also add up all the partial pressures:

P_Total = n_A + n_B + … x (RT / V)