1.3 Density and kinetic theory ⚖️

Density

how closely packed particles are; the amount of mass per unit volume

How does the spacing of particles affect density

closer together have higher density

How to change density

change temperature or state of material

Relationship between volume and mass

as mass increases, volume also increases

How the particles in a solid are arranged

• sit very closely together in a regular arrangement and fixed position

• vibrate but do not move

• held together by strong forces

Shape and volume of solids

fixed shape and volume at high density

How the particles in a liquid are arranged

• sit close together with some gaps and are randomly arranged

• can move past each other because of the gaps

• enough energy to prevent forces holding them in a regular arrangement

Shape and volume of liquids

fixed volume but take on shape of their container at medium density

How the particles in a gas are arranged

• much further apart and are randomly arranged

• move quickly and randomly in all directions

• free to move because the forces are weak

Shape and volume of gases

completely fill and have volume of their container at low density

The equation linking density, mass and volume

density = mass ÷ volume

Unit for density

Kilograms per cubic metre (kg/m³)

Unit for volume

Cubic metres (m³)

1 kilogram (kg) is equal to

1000 grams (g)

1 cubic metre (m³) is equal to

1,000,000 cubic centimetres (cm³)

1 gram per cubic centimetre (g/cm³) is equal to

1000 kilograms per cubic metre (kg/m³)

How to tell block of lead and block of wood apart (without weighing)

lead will be smaller as it has higher density

Volume of a regular substance

length * breadth * height

Volume of an irregular substance

Volume of stone = Final Volume – Initial Volume

Volume using displacement can

1. Place the stone on the top pan balance and measure its mass

2. Fill the displacement can until the water is level with the bottom of the pipe

3. Place a measuring cylinder under the pipe ready to collect the displaced water

4. Carefully drop the stone into the can and wait until no more water runs into the cylinder

5. Measure the volume of the displaced water

6. Use the measurements of mass and volume to calculate the density of the stone

When looking at measurements

always read meniscus at eye level