Molecules & Matter

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FreeScienceLessons · AQA PhysicsDensity and States of Matter

Cognito · AQA PhysicsSpecific Latent Heat

Key facts

Density and states of matter

Density = mass ÷ volume (ρ = m/V). Units: kg/m³ or g/cm³.
Solid > liquid > gas in density (usually). Water is an exception — ice is less dense than liquid water.
Solid: particles close together, regular arrangement, vibrate in fixed positions.
Liquid: particles close, random arrangement, move around each other.
Gas: particles far apart, random, move freely at high speed.

Specific latent heat

Specific latent heat (L) = energy needed to change state of 1 kg without temperature change.
E = mL (energy = mass × specific latent heat).
Latent heat of fusion (Lf) — melting/freezing.
Latent heat of vaporisation (Lv) — boiling/condensing.
During a change of state, temperature stays constant — energy changes bonds not temperature.
Water: Lf = 334,000 J/kg. Lv = 2,260,000 J/kg.

Gas pressure and temperature

Gas particles move randomly and collide with container walls — creating pressure.
Temperature ↑ → particles move faster → more/harder collisions → pressure ↑
At constant volume: P ∝ T (pressure is proportional to absolute temperature in kelvin).
Convert: K = °C + 273.
P₁/T₁ = P₂/T₂ (constant volume).
Absolute zero = 0 K = −273°C — particles have minimum energy.

Required Practical — density

Regular solid: use ruler to measure dimensions → calculate volume → use balance for mass.
Irregular solid: use displacement can/measuring cylinder — water displaced = volume.
Liquid: measure volume in measuring cylinder, mass from balance.
Density = mass ÷ volume.

Exam questions — 5 questions · 14 marks

1 markDensity calculationAQA 8463 P1 style

A block of metal has a mass of 540 g and a volume of 20 cm³. What is its density?

A 27 g/cm³

B 10,800 g/cm³

C 0.037 g/cm³

D 520 g/cm³

4 marksSpecific latent heat calculationAQA 8463 P1 style

Calculate the energy needed to completely melt 0.5 kg of ice at 0°C. (Latent heat of fusion of water = 334,000 J/kg) Then calculate the additional energy needed to heat the resulting water from 0°C to 100°C. (SHC of water = 4200 J/kg°C) (4 marks)

Hint: Two separate calculations: (1) melting → E = mL. (2) heating water → E = mcΔθ. Add them together.

+40 XP

3 marksGas pressure calculationAQA 8463 P1 style

A gas in a sealed container has a pressure of 200,000 Pa at a temperature of 27°C. Calculate the pressure when the temperature is increased to 127°C. (3 marks)

Hint: ALWAYS convert °C to K (add 273) before using gas laws. Then P1/T1 = P2/T2.

+30 XP

1 markAbsolute zeroAQA 8463 P1 style

What is absolute zero?

A The temperature at which water freezes — 0°C

B The lowest possible temperature (0 K = −273°C) at which particles have minimum kinetic energy

C The temperature at which all gases condense to liquid

D The temperature at which a gas has zero density

Molecules & Matter

Density and states of matter

Specific latent heat

Gas pressure and temperature

Required Practical — density

Module complete! 🎉