3.2 Changes of State

During a change of state, matter changes from one physical form to another. Changes of state are caused by a transfer of energy.

During a change of state, the energy of a substance changes. The identity of a substance does not change during a change of state.

Ex. Ice and liquid water are the same substance

You can change the state of a substance by adding or removing energy. Adding energy causes the particles of a substance to move more quickly. Removing energy causes the particles of a substance to move more slowly.

For example, you can add energy to a substance by heating it.

We know that when you add energy to a substance, the particles in the substance move more quickly. Because there is energy being added, there is an increase in kinetic energy of the particles.

Remember that temperature is a measure of the average kinetic energy of particles in a substance

Melting is the change in state from a solid to a liquid.

Evaporation is the change in state from a liquid to a gas. Boiling is evaporation that happens throughout a liquid at a specific temperature and pressure.

Sublimation is the change in state from a solid to a gas. Ex. Dry ice changes to a gas at room temperature.

Condensation is the change in state from a gas to a liquid. Condensation often happens when a gas touches a cool surface

Condensation point is the temperature at which a gas becomes a liquid.

Freezing is the change in state from a liquid to a solid. The temperature at which a substance freezes is its freezing point (same as its melting point)

When a substance loses or gains energy, either its temperature changes or its state changes. These two changes do not happen at the same time.

The temperature of a substance does not change during a change of state.

During a chemical or physical change, mass cannot be created or destroyed.

This can be described as the law of conservation of mass.

Just like mass, energy cannot be created or destroyed during a physical or chemical change.

This is known as the law of conservation of energy.

The total amount of energy before the change must equal the total amount of energy after the change.