Changes of State Section 4.3

What are Changes of State? Physical Changes Reversible changes Examples: Melting Freezing Sublimation Deposition Condensation Vaporization

Energy, Temperature & Changes of State Energy is always involved in changes of state. Mater either loses or absorbs energy when it changes state. Temperature – the average kinetic energy of the particles of matter.

Changes Between Liquids and Solids Freezing – liquid changing into a solid Liquid particles lose energy until they no longer slide past each other. Once in a fixed position they become a solid Freezing point – the temperature at which a liquid changes into a solid Example: Water 0°C (32°F)

Melting Melting – when solid changes into a liquid. Melting point – the temperature at which a solid changes to a liquid. Melting point is the same as the freezing point. Heat of fusion - the amount of energy required to change a substance from the solid phase to the liquid phase at its melting point

Changes Between Liquids and Gases Vaporization – liquid changes to a gas point at which the liquid breaks free of all attractive forces and changes into a gas 2 ways evaporation (happens at the surface of the liquid) particles break away into the air without boiling boiling (throughout entire substance)

Boiling point Heat of vaporization the temperature at which the pressure of the vapor in the liquid is equal to the external pressure acting on the surface of the liquid Heat of vaporization the amount of energy required for the liquid at its boiling point to become a gas

Condensation Condensation – gas changes to a liquid Water vapor cools, loses energy, forms droplets Examples: fog on bathroom mirror

Changes Between Solids and Gases Sublimation – solids change directly to a gas (without going through being a liquid) Example: Dry ice

Deposition Deposition – gas changes directly to a solid without going through the liquid state. Example: frost

Heating Curve or PHASE DIAGRAMS Temperature remains constant during a change in state.