CHANGES OF STATE

Physical Science

Chapter 2.3

Objectives1. Describe how energy is involved in changes of

state.

2. Describe what happens during melting and freezing.

3. Compare evaporation and condensation.

4. Explain what happens during sublimation.

5. Identify the two changes that can happen when a substance loses or gains energy.

Bellringer

Write a description of what must be done to liquid water to change it to ice or to change it to steam. Based on your explanation, predict what must happen to cause matter to change state.

Energy and changes of state Change of state

change of a substance from one physical form to another.

Particles move differently depending on the state of the substance.

Particles also have different amounts of energy when the substance is in different states.

Melting: Solid to Liquid

Melting change of state from a solid to a liquid.

Melting point The temperature at which a solid changes to a liquid

Adding Energy For a solid to melt, particles must overcome their

attractions to each other. At the melting point, any energy added is used to

overcome attractions between particles.

Freezing: Liquid to Solid

Freezing Change of state from a liquid to a solid.

Freezing point Temperature at which a liquid changes to

a solid. Removing Energy

When a liquid is at its freezing point, removing energy will cause the particles to begin locking into place.

Evaporation: Liquid to Gas Evaporation

Change of state from a liquid to a gas. Evaporation can occur at the surface of a

liquid that is below its boiling point. Boiling

Change of a liquid to a gas throughout the liquid.

boiling point Temperature at which a liquid boils.

Effects of Pressure on Boiling Point The boiling point of a liquid decreases as

atmospheric pressure decreases. Atmospheric pressure is caused by the weight

of the gases in the atmosphere. Atmospheric pressure is lower at higher

elevations. So, the boiling point is lower on top of

mountains than it is at sea level.

Condensation: Gas to Liquid Condensation

change of state from a gas to a liquid. Condensation point

the temperature at which the gas becomes a liquid.

Removing Energyslows the movement of gas particles which

allows them to clump together.

Sublimation: Solid to Gas

Sublimation Change of state in which a solid changes

directly into a gas. Must Gain Energy

For sublimation to occur, the attractions between the particles must be completely overcome.

Change of Temperature vs. Change of State

When most substances lose or gain energy 2 Possibilities:

1. temperature change

2. state change Temperature of a substance does not

change until a change of state is complete.