CHAPTER 12: Gases & Kinetic Molecular Theory

What are the four measurable properties of gases?

Pressure (P), Volume (V), Temperature (T), and moles (n).

What is pressure?

Force per unit area exerted by gas particles on container walls.

SI unit of pressure?

1 Pascal (Pa) = 1 N/m².

Other common pressure units?

mmHg, Torr, atm, psi.

Conversion: 1 atm = ?

760 mmHg = 760 Torr

What is Kinetic Molecular Theory?

A model of gases where particles move constantly and behave like tiny billiard balls.

Two key assumptions of KMT?

• Particles have no volume (point masses)

• No attractive or repulsive forces; collisions are perfectly elastic.

What causes gas pressure according to KMT?

Elastic collisions of particles with container walls.

Relationship between temperature and particle speed?

Higher T → higher kinetic energy → faster particles.

Boyle’s Law states?

At constant T and n, P ∝ 1/V.

Equation for Boyle’s Law?

P₁V₁ = P₂V₂

KMT explanation for Boyle’s Law?

Decreasing volume → more collisions → higher pressure.

Charles’ Law states?

At constant P and n, V ∝ T(K).

Equation for Charles’ Law?

V₁/T₁ = V₂/T₂

Why temperature must be in Kelvin?

Kelvin scale makes volume proportional to absolute temperature.

Absolute zero in °C?

–273.15°C

Avogadro’s Law states?

At constant T and P, V ∝ n.

Meaning of Avogadro’s principle?

Equal volumes of gases contain equal numbers of particles (same T & P).

Dalton’s Law states?

Total pressure = sum of partial pressures.
Ptotal = PA + PB + ...

Why do partial pressures add?

Gas particles act independently of each other.

Ideal Gas Law equation?

PV = nRT

Gas constant R values?

0.08206 L·atm/mol·K
8.314 J/mol·K

When does ideal gas law apply best?

High temperature, low pressure.

What is STP?

1 atm and 273 K

Molar volume at STP?

22.4 L per mole

Root-mean-square velocity (v₍rms₎) depends on what?

↑ Temperature → ↑ v
↑ Molar mass → ↓ v

Which gas travels fastest: He, Ne, Ar, Xe?

He (lowest molar mass)

What is diffusion?

Gas spreading from high to low concentration.

What is effusion?

Gas escaping through tiny hole into empty space

Graham’s Law of Effusion?

Rate ∝ 1/√MW
Rate₁/Rate₂ = √(MW₂/MW₁)

When do gases deviate from ideal behavior?

Low temperature and high pressure.

Why do real gases deviate?

• Real particles have volume

• Real particles experience attractive forces

What is the Van der Waals equation used for?

To correct for real gas behavior.

What do Van der Waals constants represent?

a: Intermolecular attractions
b: Particle volume

Relationship between volume and pressure?

Inversely proportional.

Relationship between temperature and volume?

Directly proportional

Relationship between moles and volume?

Directly proportional.

What happens to gas speed when T increases?

Speed increases.

Most ideal conditions?

High T, low P.