L10 - Physicochemical behaviour of gases in solution

Question 1

Ideal Gas Law equation

Answer 1

PV = nRT

P = pressure of gas (1Pa = 1 Nm-2)
V = volume of gas container (metres cubed -m3)
n = number of moles of gas (Av. constant = 6.022 × 10²³)
R = Gas Constant (unit given in exam)
T = temperature of gas in container (273K = 0oC)

Question 2

Dalton’s law equation (partial pressures)

Answer 2

p = p(gas) + p(gas) + P(gas)…

p = overall gas pressure
p(gas) = partial gas pressure

• Total pressure of mixture of gases is equal to sum of partial pressures of individual gases in mixture

Question 3

Raoul’s Law equation (vapour pressure)

Answer 3

𝑝(𝑖) = 𝑝(𝑖)∗ x 𝑥(𝑖)

𝑝(𝑖) = partial vapour pressure of a component i in the vapour phase
𝑝(𝑖)∗ = vapour pressure of the pure component
𝑥(𝑖) = mole fraction of that component in solution

• Vapour pressure – pressure exerted by vapour in thermodynamically equilibrium with its condensed phases (solid or liquid) – fixed T + closed system
• Assumed that intermolecular forces between unlike molecules are equal to those between similar molecules - conditions of an ideal solution.

Question 4

Henry’s Law equation (gas solubility)

Answer 4

P = Hv x M

P = partial pressure
Hv = Henry’s law proportionality constant
M = molar concentration of gas in solution

• At constant T, the amount of a given gas that dissolves in a liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid
• Doubling P = doubles M (since Hv is a constant)
• Different gases have different solubilities - affects rate