Section 12.1 - Gases & Kinetic Molecular Theory

What is the kinetic molecular theory?

A theory that describes the behavior of matter in terms of particles in motion

What are gas particles like according to the theory?

Small, constantly moving, far apart, and expierencing elastic collisions.

What is an elastic collision?

A collision where no kinetic energy is lost.

How is temperature related to kinetic energy?

Temperature measures the average kinetic energy of particles (measured in Kelvin).

What is diffusion?

Movement of one material through another.

What is effusion?

When a gas escapes through a tiny opening.

What does Graham’s Law state?

The rate of effusion is inversely proportional to the square root of the molar mass.

What causes gas pressure?

Gas pressure is caused by the collisions of gas particles with the walls of a container.

What is atmospheric pressure?

Pressure from the air in Earth’s atmosphere, lower at high altitudes.

What instruments measure pressure?

Barometer (air pressure), Manometer (gas in container).

What is the unit of pressure?

Pascal (Pa); also use atm, mm Hg, and kPa.

1 atm = ?

760 mm Hg = 101.3 kPa

What is Dalton’s Law?

Total pressure of a gas mixture = sum of partial pressures:
Pₜ = P₁ + P₂ + P₃ + ...

What determines a substance’s state at a given temperature?

Intermolecular forces.

What are dispersion forces?

Weak forces from temporary shifts in electron density.

What are dipole-dipole forces?

Attractions between opposite ends of polar molecules.

What are hydrogen bonds?

Strong dipole-dipole forces involving H bonded to F, O, or N.

What is viscosity?

Resistance to flow; increases with stronger forces and larger molecules.

What reduces viscosity?

Increasing temerature

What is surface tension?

Energy needed to increase surface area of a liquid.

What do surfactants do?

Lower surface tension.

What is cohesion vs adhesion?

Cohesion = attraction between same molecules; Adhesion = between different molecules.

What is capillary action?

Liquid rising in a narrow tube due to cohesion & adhesion.

What is the difference between crystalline and amorphous solids?

Crystalline: ordered structure; Amorphous: random particle arrangement.

What causes a phase change?

Addition or removal of energy.

What’s the melting point?

Temperature where a solid becomes a liquid.

What is vaporization vs evaporation?

Vaporization = liquid to gas; Evaporation = at surface only.

What is vapor pressure?

Pressure of vapor above a liquid in a closed container.

What is the boiling point?

When vapor pressure = atmospheric pressure.

What is sublimation and deposition?

Sublimation = solid to gas; Deposition = gas to solid.

What is the triple point?

The condition where all three phases (solid, liquid, gas) coexist.

What is the critical point?

Where liquid and gas phases become indistinguishable.