CHEM 155 - Basic Physical Chemistry Summary

States of Matter

  • Matter exists as gas, liquid, solid.

  • Gas molecules are widely separated and move freely.

  • Liquids have touching molecules allowing movement.

  • Solids have fixed, ordered positions; particles vibrate.

General Characteristics of Gases

  • Expansibility: Gases expand to fill their container.

  • Compressibility: Gases can be compressed easily.

  • Diffusibility: Gases diffuse rapidly to form a mixture.

  • Pressure: Gases exert pressure uniformly in all directions.

  • Effect of Heat: Heating gas increases pressure; volume can expand.

Gas Properties

  • Key measurable properties: Temperature, Pressure, Volume, Moles.

Gas Volume

  • Volume in litres (l), millilitres (ml); 1 l = 1000 ml.

  • SI unit is cubic metre (m³).

Gas Pressure

  • Defined as force per unit area from molecular impacts.

  • Measured using mercury manometers or barometers.

  • 1 at = 760 mm Hg = 760 torr = 1.013 x 10⁵ Pa.

Gas Temperature

  • Measured in Celsius (°C) and converted to Kelvin (K) using K = °C + 273.

Moles of Gas

  • Number of moles (n) calculated as n = m / M, where m = mass, M = molar mass.

Gas Laws

  • Gas behavior is governed by relationships called gas laws.

Boyle’s Law

  • At constant T: V ∝ 1/P; PV = k (constant).

Charles’ Law

  • At constant P: V ∝ T; V/T = k (constant).

Combined Gas Law

  • Relates pressure, volume, and temperature: (PV/T = k).

Gay Lussac's Law

  • At constant volume: P ∝ T; P/T = k (constant).

Avogadro’s Law

  • Equal volumes of gases at same T and P contain equal molecules: V ∝ n.

Ideal Gas Law

  • (PV = nRT); relates P, V, T, and n with R as gas constant.

Kinetic Molecular Theory (KMT)

  • Explains gas behavior; gas molecules are in constant motion.

Ideal vs. Real Gases

  • Ideal gases obey KMT perfectly; real gases deviate under extreme conditions.

van der Waals Equation

  • Modifies ideal gas equation to account for intermolecular forces and molecular volumes:
    (P + \frac{an^2}{V^2}(V-nb) = nRT).

Critical Phenomena

  • Critical temperature (Tc), pressure (Pc), and volume (Vc) define liquefaction limits.

Collision Theory

  • Mean free path and collision frequency are fundamental properties of gases.

Compressibility Factor (Z)

  • Measures deviation of real gas from ideal behavior; Z = PV/(RT).

  • Z < 1 indicates attractive forces; Z > 1 indicates repulsive forces.