Changes of State Chapter 4-2

Changes of State A change of state is the conversion of a substance from one physical form to another. All the changes are physical changes.

The identity of the substance does not change.

During a change of state, the energy of a substance changes. The energy of a substance is caused by the motion of the particles.

MELTING: Solid to Liquid Melting point is the temperature at which a substance melts. The melting point is different for all substances. For a solid to melt, energy must be absorbed to make the molecules move faster.

FREEZING: Liquid to Solid Freezing point is the temperature that a liquid becomes a solid. Energy is removed during freezing.

EVAPORATION: Liquid to Gas Evaporation is the change of state from liquid to a gas. It happens at the surface. Sweat evaporating cools your body.

BOILING: Liquid to Gas Boiling is also a change from a liquid to a gas at 100 degrees celsius. Large groups of molecules escape rather than just a few at a time. Water will boil at a lower temp. at higher altitudes because the atmospheric pressure is less.

CONDENSATION: Gas to Liquid The condensation point is the temp. at which a gas becomes a liquid. Beads of water form when water vapor in the air contacts a cool surface.

SUBLIMATION: Solid to Gas Sublimation is the change of state in which a solid changes directly to a gas. Dry ice goes through sublimation instead of melting into a liquid.

The ice, liquid water, and steam are all the same substance.

Temperature and Changes of State When substances gain or lose energy, its temp. changes or its state changes. When the temp. changes so does the particle movement. Higher temp. = faster movement Lower temp. = slower movement

The temperature remains the same at the horizontal lines while energy is added constantly.

Stop here and do chart.