AQA GCSE Changes of state

AQA GCSE Changes of State

Changes of State

A change of state is a physical change, this means that the change is reversible, when the process is reversed the material regains its original properties. 

If ice is melted to form liquid water and then frozen to reform ice, the ice that is formed has the same properties as the ice at the start.

Change of state triangle

Learn the names of the different processes

Diagram to show the changes of state and the names of the processes for each change of state.

In the 

Key terms:

Melting is when a solid forms a liquid

Freezing is when a liquid forms a solid

Boiling or evaporation is when a liquid forms a gas or vapour.

Condensing is when a gas forms a liquid.

Sublimation is when  solid turns directly into a gas, missing out the liquid state. Iodine and solid carbon dioxide can both undergo sublimation. 

Dry ice (solid carbon dioxide) on a spoon undergoing sublimation:

Dry ice, solid carbon dioxide on a spoon undergoing sublimation

 

Solid dark grey iodine undergoing sublimation to form purple vapours:

iodine undergoing sublimation

 

Changes of state and mass

When a substance changes state, the number of particles will not change, so the mass of the substance will not change. 

If 100g of ice is melted, then 100g of liquid water is formed. When this water is boiled, 100g of steam is formed.

Practice Questions

1.Explain what is meant by a change of state being a physical change. 

2. In the winter liquid water forms on the surface of windows. State the name of the process that is responsible for the liquid water forming

3. 1500g of liquid propane is allowed to evaporate. State the mass in kg for the total propane vapours formed.

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