Did this video help you?
Changes of State (Edexcel GCSE Physics)
Revision Note
Did this video help you?
Changes of State
- When a substance changes state, the number of molecules in that substance doesn’t change and so neither does its mass
- The only thing that changes is its energy
- Unlike chemical changes, changes of state (a type of physical change) are reversible
- In a solid:
- The molecules are very close together and arranged in a regular pattern
- The molecules vibrate about fixed positions
- In a liquid:
- The molecules are still close together (no gaps) but are no longer arranged in a regular pattern
- The molecules are able to slide past each other
- In a gas:
- The molecules are widely separated - about 10 times further apart in each direction
- The molecules move about randomly at high speeds
- There are six changes of state that can occur between solids, liquids and gases:
- Melting - When a solid turns into a liquid (e.g. ice to water)
- Boiling - When a liquid turns into a gas (evaporating)
- Condensing - When a gas turns into a liquid
- Freezing - When a liquid turns into a solid
- Subliming - When a solid turns into a gas
Diagram showing the arrangement and motion of different states of matter
Worked example
A student measures the mass of a beaker of water twice, leaving 24 hours between the readings. The temperature in the room remained constant between readings, however, they notice a decrease in the mass of the beaker of water.Which of the following is not a correct conclusion that can be drawn from the experiment?
A The difference in mass is equal to the mass of the water that evaporated
B The total energy within the beaker decreased
C The density of water in the air increased
D The total number of water molecules in the air and water decreased
ANSWER: D
- A is true because the mass lost from the beaker is due to those water molecules evaporating
- B is true because evaporation causes the most energetic particles to leave the beaker
- The total number of particles in the beaker decreased
- C is true because additional water molecules were added to the air, without a significant change in the volume of the air
- D is not true because no mass is lost during evaporation - it is only changed from a liquid to gas state
You've read 0 of your 10 free revision notes
Unlock more, it's free!
Did this page help you?