Latent Heat & Phase Change — A/L Physics

What must I remember about Latent Heat & Phase Change?

• Phase Changes: Isothermal processes occurring at constant temperature: Melting/Freezing, Vaporization/Condensation, Sublimation.
• Latent Heat Definition: Heat energy absorbed or released per unit mass of a substance during a phase change at constant temperature and pressure: Q = m * L.
• Specific Latent Heat of Fusion (L_f) vs Vaporization (L_v): For water: L_f ≈ 3.33 × 10⁵ J/kg (ice-water at 0 °C); L_v ≈ 2.26 × 10⁶ J/kg (water-steam at 100 °C); L_v is much greater than L_f because vaporization requires breaking intermolecular hydrogen bonds completely and doing work against atmospheric pressure.
• Cooling Curves: Temperature vs time plot; horizontal plateau indicates latent heat phase transition where temperature remains strictly constant while substance transforms.

Test yourself (1 minute)

1. Regelation of Ice

   Melting point of ice decreases under increased pressure; when pressure is relieved, water refreezes (demonstrated by wire weighted across an ice block).

2. Effect of Impurities

   Dissolved impurities lower the freezing point (depression of freezing point, e.g., salting roads in winter) and elevate the boiling point.

3. Supercooling

   Phenomenon where a liquid cools below its normal freezing point without solidifying, due to lack of nucleation sites; instantly crystallizes upon disturbance.

Practise Latent Heat & Phase Change questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 4: Thermal Physics

What should I study first?

What comes next?

Next in the syllabus

Where does Latent Heat & Phase Change fit in the syllabus?

Unit 4.5 · Year 1 · Term 2