Chapter 4: Heat

4.1 Thermal Equilibrium

• When two objects are in thermal contact, heat flows from the hotter to the colder object until their temperatures are equal and net heat transfer becomes zero — this is thermal equilibrium. (p.121)
• Examples: a clinical thermometer under the tongue, food cooling in a refrigerator, ice cubes cooling a drink, a cake baking in an oven. (p.122)
• Calibrating a liquid-in-glass thermometer uses two fixed points: 0°C (melting ice) and 100°C (boiling water). θ = (Lθ/L100) × 100°C. (p.124)

4.2 Specific Heat Capacity

• Heat equation: Q = mcΔθ (p.127)
• Specific heat capacity, c = Q / (mΔθ) (p.127)
• Determined experimentally using an immersion heater: c = Pt / (mΔθ), since Q = Pt. (p.129)
• Applications: metal woks (low c, heat quickly) vs clay pots (high c, retain heat); car radiator systems (water's high c used as coolant); wooden houses (insulation); land/sea breezes (land has a lower specific heat capacity than sea). (p.132)
• For heat exchange between two substances: heat lost = heat gained (Q₁ = Q₂). (p.135)

4.3 Specific Latent Heat

• Latent heat is heat absorbed or released during a change of phase, without a change in temperature. (p.137)
• Specific latent heat, l = Q/m (p.137)
• Specific latent heat of fusion, l_f: heat absorbed during melting or released during freezing of 1 kg of substance, without temperature change. (p.138)
• Specific latent heat of vaporisation, l_v: heat absorbed during boiling or released during condensation of 1 kg of substance, without temperature change. (p.138)
• Heating curve: solid → melting (constant temperature) → liquid → boiling (constant temperature) → gas. (p.138)
• For a given substance, specific latent heat of vaporisation is generally larger than specific latent heat of fusion. (p.140)
• Applications: refrigerator cooling cycle (compressor, condenser, expansion valve, evaporator); cooling effect of sweat evaporation. (p.145)
• Formula for electrical heating causing phase change: Pt = ml (p.146)

4.4 Gas Laws

• Based on the Kinetic Theory of Gas: pressure arises from molecular collisions with container walls; temperature relates to average kinetic energy of molecules; volume equals the volume of the container. (p.148)
• S.I. units: Pressure — pascal (Pa); Temperature — kelvin (K); Volume — cubic metre (m³). (p.149)
• Boyle's Law: pressure is inversely proportional to volume for a fixed mass of gas at constant temperature: P ∝ 1/V; P₁V₁ = P₂V₂. (p.151)
• Absolute zero = −273°C = 0 K. Conversion: T(K) = θ(°C) + 273. (p.155)
• Charles' Law: volume is directly proportional to absolute temperature for a fixed mass of gas at constant pressure: V ∝ T; V₁/T₁ = V₂/T₂. (p.156)
• Gay-Lussac's (Pressure) Law: pressure is directly proportional to absolute temperature for a fixed mass of gas at constant volume: P ∝ T; P₁/T₁ = P₂/T₂. (p.160)