Particle model of matter

Question 1

What are the states of matter and their characteristics?

Answer 1

• There are three states: solids, liquids and gases.
• Solids and liquids are incompressible (cannot be squashed) because there are no gaps between particles in them.
• Solids contain particles in a fixed pattern and have a fixed size and shape.
• Liquids have a fixed size but contain particles that are free to move, allowing them to change shape to fit their container.
• Gases have large gaps between particles, making them compressible and enabling them to change size and shape.

Question 2

What is density and how do you find it?

Answer 2

• The density of a material is its mass per unit volume.
• density (p, measured in kilograms per metre cubed) = mass (m, measured in kilograms) divided by volume (V, measured in metres cubed.)

Question 3

What is a change of state?

Answer 3

• As energy is added to a system, its temperature will increase.
• At the melting or boiling point, the energy being added causes the substance to change state not temperature.
• A change of state is reversible.
• It is a physical change that alters the internal energy not the temperature or mass. It is not a chemical change.
• energy for a change of state = mass multiplied by specific latent heat (E = mL).

Question 4

What is a latent heat of fusion, vaporisation, and (de)sublimation?

Answer 4

• The latent heat of fusion is the energy needed for a substance to change state from solid to liquid (melt).
• The latent heat of vaporisation is the energy needed for a substance to change state from liquid to gas (evaporate).
• The horizontal parts of heating and cooling graphs indicate where energy is being used to change state.
• At certain pressures, some substances have a boiling point that is the same as their melting point.
• These substances change from a solid to a gas without having a liquid phase in the middle. This is called sublimation. The reverse proceess, changing from a gas to a solid, is called desublimation.