The Gas Phase, Phases, and Phase Changes

MCAT Prep: General Chemistry Part 5

760; 760; 101,325

1 atm = ___ mmHg = ____ torr = ____ Pa

0; 273; 1

STP: ___ degrees C or ___ K and ___ atm

STP

generally used for gas law calculations

25; 298; 1; 1

Standard conditions: ___ degrees C or ___ K, ___ atm, and ____ M concentrations

standard conditions

used when measuring standard enthalpy, entropy, Gibbs free energy, and electromotive force

Boyle’s law

PV = k or P₁V₁ = P₂V₂

Charles’s law

V/T = k or V₁/T₁ = V₂/T₂

Gay-Lussac’s law

P/T = k or P₁/T₁ = P₂/T₂

Avogadro’s principle

n/V = k or n₁/V₂ = n₂/V₂

Combined gas law

integrates Boyle’s law, Charles’s law, and Gay-Lussac’s law

(P₁V₁)/T₁ = (P₂V₂)/T₂

Ideal gas law

PV = nRT

closer; smaller

Decreasing the volume of a sample of gas makes it behave less ideally because the individual gas particles are in _______ proximity in a ________ volume

increases

As the pressure of a gas ________, the particles are pushed closer and closer together. At moderately high pressure, a gas’s volume is less than would be predicted by the ideal gas law due to intermolecular attraction.

decreases

As the temperature of a gas ________, the average velocity of the gas molecules decreases and the attractive intermolecular forces become increasingly significant

smaller

Increases intermolecular attraction causes the gas to have a ________ volume than would be predicted.

larger

At extremely low temperature, the volume of the gas particles themselves cause the gas to have a _________ volume than would be predicted.

22.4

1 mole of gas at STP in L

Dalton’s law of partial pressures

states that the total pressure of a gaseous mixture is equal to the sum of the partial pressures of the individual components

P_T = P_A + P_B + P_C + …

P_A = P_TX_A

where X_A = n_A (moles of A) / n_T (total moles)

Kinetic molecular theory of gases

an explanation of gaseous molecular behavior based on the motion of individual molecules

Average molecular speed

the temperature of the system dictates the speed of a gas molecule, since it is a measure of the average kinetic energy

K = (1/2)mv² = (3/2)k_BT

Colligative properties

these are physical properties derived solely from the number of particles present, not the nature of those particles. These properties are usually associated with dilute solutions. Molarity (m) is often used, in addition to the van ‘t Hoff factor (i) for ionic compounds

Freezing point depression

ΔT_f = iK_fm

Boiling point elevation

ΔT_b = iK_bm

Osmotic pressure

Π = MRT

Vapor pressure lowering (Raoult’s law)

P_A = X_AP_A°

P_B = X_BP_B°

Ideal solutions

solutions that obey Raoult’s law

Diffusion

occurs when gas molecules distribute through a volume by random motion

Effusion

the flow of gas particles under pressure from one compartment to another through a small opening

Diffusion and effusion formula

r₁/r₂ = √(m₂/m₁)