Thermal Properties And TemperatureCopy

Cheat Sheet: Thermal Expansion, Specific Heat Capacity, and Change of State (O Level / IGCSE Physics)

2.2.1 Thermal Expansion

1. Applications and Consequences of Thermal Expansion

• Expansion occurs when a material is heated; particles move faster and push further apart

Examples:

• Liquid-in-glass thermometer: liquid (mercury/alcohol) expands with temperature → rises in capillary tube
• Bridges: have expansion gaps to prevent damage from heat
• Overhead power lines: sag more in summer due to expansion
• Jar lids: loosened by heating the metal lid (expands more than the glass)

2. Particle Explanation of Thermal Expansion

• Solids: particles vibrate faster but stay in fixed positions; slight expansion
• Liquids: particles move more freely; more noticeable expansion
• Gases: particles move rapidly and freely; greatest expansion

Order of Expansion (from least to greatest):
Solids < Liquids < Gases

3. Temperature Conversion

• Kelvin to °C: θ = T − 273
• °C to Kelvin: T = θ + 273

2.2.2 Specific Heat Capacity

1. Internal Energy and Temperature

• Heating an object increases its internal energy, which increases the average kinetic energy of its particles

2. Definition of Specific Heat Capacity

• Specific heat capacity (c) = energy required to raise the temperature of 1 kg of a substance by 1°C (or 1 K)
• Equation:
  c = ∆E / (m × ∆θ)
  where:
  ∆E = energy supplied (J)
  m = mass (kg)
  ∆θ = temperature change (°C or K)
  c = specific heat capacity (J/kg·°C)

3. Experiments to Measure Specific Heat Capacity

For a Solid:

• Use a block with a heater and thermometer
• Measure initial temperature
• Supply energy using an electric heater (record current & voltage)
• Use stopwatch to measure time
• Calculate energy: E = V × I × t
• Measure temperature rise
• Apply: c = ∆E / (m × ∆θ)

For a Liquid:

• Use an insulated beaker with heater and thermometer
• Stir the liquid for uniform heating
• Measure mass, temperature change, and electrical energy supplied
• Apply same formula as above

2.2.3 Melting, Boiling & Evaporation

1. Change of State Without Temperature Change

• Melting, boiling, condensation, freezing involve energy transfer
• Energy is used to break/form bonds between particles
• No change in temperature during state change

2. Melting & Boiling Points of Water (Standard Pressure)

• Melting point: 0°C
• Boiling point: 100°C

3. Boiling vs Evaporation

4. Evaporation (Particle Explanation)

• High-energy particles at the surface escape
• Remaining particles have lower average energy → temperature drops

5. Factors Affecting Evaporation

• Temperature: higher = faster evaporation
• Surface Area: larger = more evaporation
• Air Movement: more wind = faster evaporation
• Humidity: less humidity = faster evaporation

6. Evaporation Causes Cooling

• Fastest (most energetic) particles leave → average energy decreases → cooling effect

7. Latent Heat

• Latent heat = energy needed to change state without changing temperature
• Explanation (Particles):
  • Energy goes into breaking intermolecular bonds, not into kinetic energy
  • E.g. melting: solid to liquid → bonds loosen
  • Boiling: liquid to gas → particles fully separate