Kinetic Theory of Matter and Gas Laws

This topic explores the behavior of matter at the molecular level and the mathematical laws that govern the physical properties of gases.

1. Kinetic Theory of Matter

The kinetic theory states that all matter is composed of tiny particles (atoms, molecules, or ions) that are in constant, random motion.

• Solids: Particles are closely packed in a fixed lattice. They vibrate about fixed positions but do not move from place to place. This gives solids a definite shape and volume.
• Liquids: Particles are close together but can move past one another. This allows liquids to flow and take the shape of their container while maintaining a constant volume.
• Gases: Particles are far apart and move rapidly in all directions. Gases have no definite shape or volume and expand to fill any container.

Changes of State

• Melting: Solid to liquid. Heat energy increases molecular vibration until the lattice breaks.
• Vapourization/Boiling: Liquid to gas. Molecules gain enough kinetic energy to overcome intermolecular forces and escape into the air.
• Freezing: Liquid to solid. Loss of heat energy causes particles to slow down and form a fixed structure.
• Condensation: Gas to liquid. Cooling causes gas molecules to slow down and clump together.

Brownian Movement

The random, zigzag motion of microscopic particles (like pollen or dust) suspended in a fluid, caused by collisions with invisible, fast-moving molecules of the fluid. This is direct evidence for the kinetic theory.

2. The Gas Laws

• Boyle's Law: The volume of a fixed mass of gas is inversely proportional to its pressure at constant temperature (P1V1 = P2V2).
• Charles's Law: The volume of a fixed mass of gas is directly proportional to its absolute temperature at constant pressure (V1/T1 = V2/T2).
• Dalton's Law of Partial Pressures: In a mixture of non-reacting gases, the total pressure is the sum of the partial pressures of the individual gases.
• Graham's Law of Diffusion: The rate of diffusion of a gas is inversely proportional to the square root of its density or molar mass.
• Ideal Gas Equation: Combines Boyle's, Charles's, and Avogadro's laws: PV = nRT.

3. Relative Molecular Mass and Vapour Density

The relative molecular mass (RMM) of a gas is twice its vapour density (V.D.).

RMM = 2 x Vapour Density