States of Matter

Question 1

What is matter? (1)
What is the particle theory? (3)

Answer 1

Matter is anything with mass.

The particle theory of matter is a model that describes the arrangement and movement of particles in a substance. The model is used to explain the physical properties of solids, liquids and gases.

Explaining properties
Solids:

have a fixed volume and a fixed shape
cannot flow, because their particles cannot move from place to place
cannot be easily compressed, because their particles are close together with no space to move into
Liquids:

have a fixed volume but no fixed shape
can flow and take the shape of their container, because their particles can move around each other
cannot be easily compressed, because their particles are close together with no space to move into
Gases:

have no fixed shape or volume
can flow and completely fill their container, because their particles move quickly in all directions
can be compressed, because their particles are far apart with space to move into

Question 2

Distinguish between the three main states of matter, solid, liquid and gas in terms of their particle arrangement. Give examples of each. (6)

Answer 2

Solids have a regular, very close arrangement of atoms. For example, silver.
Liquids have a randomly arranged, close arrangement of atoms. For example, water.
Gases have a randomly arranged, far apart arrangement of atoms. For example, air.

Question 3

What is a physical change? (2)

Answer 3

Physical changes are changes such as state change and dissolving, which are reversible, and there is no change in total mass when they happen.

Question 4

Define melting, boiling, evaporation, condensation freezing and sublimation. (6)

Answer 4

Melting, evaporating and boiling
Energy must be transferred, by heating, to a substance for these changes of state to happen. During these changes the particles gain energy, which is used to break or overcome:

some of the bonds between particles during melting
all the remaining bonds between particles during evaporating or boiling
Evaporation can take place below the boiling point of a substance. This is why damp clothes dry when they are hung from a washing line. Boiling happens at the boiling point, when the rate of evaporation is at its maximum.

Condensing and freezing
Energy must be transferred from a substance to the environment for condensation and freezing to happen. During these changes of state, the particles lose energy as bonds form between the particles.

Some substances can change directly from solid to gas, or from gas to solid, without becoming a liquid in between. This is called sublimation.

Question 5

Define boiling and melting point. (2)

Answer 5

Melting point is the temperature at which a solid changes into a liquid.

Boiling point is the temperature at which a liquid changes into a gas.

Question 6

What type of energy is (usually) required for a change of state to occur? (1)

Answer 6

Thermal Energy.

Question 7

What is diffusion? (2) Bonus: why is it important? (1)

Answer 7

Diffusion is the movement of a substance from an area of high concentration to an area of lower concentration.

Diffusion occurs in liquids and gases when their particles collide randomly and spread out.

Diffusion is an important process for living things - it is how substances move in and out of cells.

Question 8

Describe gas pressure in terms of volume and temperature. (3)

Answer 8

Pressure in gases is caused by particles colliding with the walls of the container.

Gas pressure is increased when the temperature increases or the volume of the container decreases.