Changes of state and conservation of mass

In a nutshell

When a state change takes place the arrangement of particles alter. The particle arrangement will change due to a change in the particle energy.

Changes of state

Definition

A change of state refers to when one state of matter is changed into another. For a change of state to happen energy must either be supplied or given out and this will alter the arrangement of particles resulting in a change of state.

Energy in state changes

State of matter is heated (energy gain)

1.	Particles gain energy.
2.	More particle movement, forces between particles start to weaken. State will start to expand.
3.	At a certain temperature, with enough energy, particles will break free of the forces between them.
4.	State change occurs.

State of matter is cooled (energy loss)

1.	Particles lose energy.
2.	Less particle movement, forces between particles begin to strengthen.
3.	At a certain temperature, with enough energy lost, forces between particles will form.
4.	State change occurs.

Changes of state processes

Science; States of matter; KS3 Year 7; Changes of state and conservation of mass — A. Ice, B. Water, C. Water vapour

process	state change	temperature change	energy change
1. Melting	Solid to liquid	Heating	Energy gain
2. Freezing	Liquid to solid	Cooling	Energy loss
3.Evaporation/boiling	Liquid to gas	Heating	Energy gain
4. Condensation	Gas to liquid	Cooling	Energy loss
5. Deposition	Gas to solid	Cooling	Energy loss
6. Sublimation	Solid to gas	Heating	Energy gain

Note: Sublimation is very rare.

Conservation of mass

A state change does not involve a change in mass, only a change in energy.

Example

Explain what is happening to the solid particles during the melting process.

Melting will result in the heating of a solid to a liquid.
Heating will mean that the solid particles will gain energy.
Particles will begin to move more and the forces between them will weaken.
At a certain melting temperature, the forces between the solid particles will break free and a liquid will form.