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Overview
A phase change occurs when matter changes from one state to another. Common phase changes include solid to liquid, liquid to gas, gas to liquid, liquid to solid, solid to gas, and gas to solid. During a phase change, energy is transferred into or out of the substance, often without a temperature change during the transition itself.
States of Matter
The common states of matter are solid, liquid, gas, and plasma. Solids have particles arranged in relatively fixed positions, liquids flow while maintaining volume, and gases expand to fill available space.
Melting and Freezing
Melting is the change from solid to liquid. Freezing is the change from liquid to solid. These processes involve energy changes associated with particle arrangement.
Vaporization and Condensation
Vaporization changes liquid to gas. Condensation changes gas to liquid. Boiling and evaporation are forms of vaporization.
Sublimation and Deposition
Sublimation changes solid directly to gas. Deposition changes gas directly to solid. Dry ice sublimating is a common example.
Latent Heat
Latent heat is energy transferred during a phase change without changing temperature. The energy changes particle arrangement or separation rather than average kinetic energy.
Heating Curves
Heating curves show temperature changes and phase-change plateaus as energy is added. Flat regions correspond to phase changes where temperature remains constant during the transition.
Pressure Effects
Pressure affects phase changes. Boiling point, melting point, and phase stability can change when pressure changes.
Common Mistakes
A common mistake is assuming temperature always rises when heat is added. During a phase change, added energy can change state instead of temperature.
Why This Matters in Physics
Phase changes are essential for weather, climate, cooking, refrigeration, engines, materials science, biology, and planetary science.