Kinetic Theory & States of Matter – Core Vocabulary

Vocabulary flashcards covering essential terms from the lecture on kinetic theory, molecular arrangement, changes of state, and evaporation.

Matter

Anything that has mass and occupies space; exists mainly as solids, liquids, or gases.

Molecule

The smallest unit of a substance that retains its chemical properties; may contain one or more atoms.

Atom

The smallest unit of an element; combines with others to form molecules.

Kinetic (Molecular) Theory of Matter

Model stating that all matter is made of constantly moving molecules whose motion and spacing explain physical properties and changes of state.

Intermolecular Space

The empty distance between molecules; smallest in solids, largest in gases.

Intermolecular Forces

Attractive forces between molecules; strongest in solids, weakest in gases.

Cohesion (Cohesive Force)

Attraction between molecules of the same substance.

Adhesion (Adhesive Force)

Attraction between molecules of different substances, causing them to stick together.

Brownian Motion

Random zig-zag movement of microscopic particles showing molecular motion.

Solid

State of matter with closely packed molecules, fixed shape, fixed volume, and only vibrational motion.

Liquid

State with loosely packed molecules, definite volume, no fixed shape, slight compressibility, and ability to flow.

Gas

State with widely separated molecules, no fixed shape or volume, high compressibility, and free random motion.

Melting (Fusion)

Process in which a solid changes to a liquid upon heating at a fixed temperature.

Melting Point (Fusion Point)

Fixed temperature at which a solid melts to become a liquid under standard atmospheric pressure.

Freezing (Solidification)

Process in which a liquid changes to a solid upon cooling at a fixed temperature.

Freezing Point

Fixed temperature at which a liquid solidifies; numerically equal to its melting point for the same substance.

Vaporisation (Boiling)

Change of a liquid to a gas throughout the liquid at a fixed temperature called its boiling point.

Boiling Point

Fixed temperature at which a liquid boils at standard atmospheric pressure.

Condensation (Liquefaction)

Change of a gas to a liquid at a fixed temperature equal to its boiling point.

Condensation Point

Fixed temperature at which a vapour condenses to liquid; same as its boiling point.

Sublimation

Direct transition of a substance from solid to vapour without passing through the liquid state.

Sublimation Point

Fixed temperature at which a solid sublimes to vapour.

Deposition (Desublimation)

Direct change of a vapour to a solid without becoming liquid; reverse of sublimation.

Latent Heat

Heat absorbed or released during a change of state at constant temperature.

Latent Heat of Fusion

Heat required to convert 1 kg of a solid into liquid at its melting point without temperature change (e.g., ice: 3.35 × 10⁵ J kg⁻¹).

Latent Heat of Vaporisation

Heat required to convert 1 kg of a liquid into vapour at its boiling point without temperature change (e.g., water: 2.26 × 10⁶ J kg⁻¹).

Latent Heat of Sublimation

Heat absorbed when 1 kg of a sublimate solid turns directly into vapour at the sublimation point.

Evaporation

Slow transition of a liquid to vapour at any temperature below its boiling point, occurring only at the surface.

Evaporative Cooling

Temperature drop in a liquid or its surroundings due to heat absorbed during evaporation.

Volatile Liquid

Liquid that evaporates rapidly at ordinary temperatures (e.g., ether, alcohol, petrol).

Factors Affecting Evaporation

Nature of liquid, temperature, surface area, wind/air flow, and humidity collectively govern evaporation rate.

Surface Area (Evaporation Factor)

Larger exposed surface increases evaporation rate (e.g., clothes spread out to dry).

Humidity (Evaporation Factor)

Amount of water vapour in air; higher humidity lowers evaporation rate.

Wind Speed / Air Flow

Moving air carries away vapour, accelerating evaporation.

Nature of Liquid

Intrinsic properties such as intermolecular forces; weaker forces yield faster evaporation.

Temperature

Measure of average molecular kinetic energy; higher temperature speeds evaporation and increases kinetic energy.

Kinetic Energy

Energy of molecular motion; rises with temperature and is lowest in solids, highest in gases.

Compressibility

Degree to which matter volume decreases under pressure; negligible in solids, slight in liquids, high in gases.

Free Surface

Exposed upper surface of a liquid; liquids have one, gases none, solids maintain shape without one.