Thermodynamics
Temperature, heat, specific and latent heat, heat transfer, expansion and the gas laws.
Thermodynamics, summary notes
- Temperature is the average kinetic energy of particles; heat is energy in transit between bodies at different temperatures.
- Heat transfer happens three ways: conduction (through solids), convection (through fluids), radiation (no medium needed, how the sun heats a parked aircraft's skin).
- First law: energy is conserved, change in internal energy equals heat added minus work done (ΔU = Q − W).
- Second law: heat flows spontaneously from hot to cold, never the reverse without external work, why no heat engine, including a jet engine, can be 100% efficient.
- Gas laws describe how pressure, volume and temperature relate for a fixed amount of gas, relevant to gas turbine cycles, tyre inflation with temperature and oxygen bottle behaviour at altitude.
- Boyle's Law (constant T)
- P₁V₁ = P₂V₂
- Charles's Law (constant P)
- V₁/T₁ = V₂/T₂
- Gay-Lussac's Law (constant V)
- P₁/T₁ = P₂/T₂
- Combined/ideal gas law
- P₁V₁/T₁ = P₂V₂/T₂
- Heat energy
- Q = mcΔT
- Latent heat
- Q = mL
- First law
- ΔU = Q − W
- Temperature conversion
- K = °C + 273 · °F = (°C × 9/5) + 32
A gas cylinder holds 2 m³ at 100 kPa and constant temperature. It's compressed to 1 m³. Find the new pressure.
Boyle's Law: P₂ = P₁V₁/V₂ = (100 × 2)/1 = 200 kPa.
How much heat is needed to raise 5 kg of aluminium (specific heat capacity 900 J/kg·K) from 20°C to 80°C?
Q = mcΔT = 5 × 900 × (80 − 20) = 270,000 J (270 kJ).
Gas laws (PV = nRT)
Heat transfer
Specific & latent heat
Thermal expansion
Thermodynamics concept map
Thermodynamics
Thermodynamics quiz
Thermodynamics
1. How much heat is needed to raise 2 kg of water by 30 K, taking the specific heat capacity as 4200 J/kg·K?
252 kJ126 kJ8.4 kJ2. A temperature of 27 °C expressed in kelvin is:
300 K246 K27 K3. A steel bar 10 m long is heated through 50 K. Taking the coefficient of linear expansion as 12 × 10⁻⁶ per K, the expansion is:
6 mm60 mm0.6 mm4. The SI unit of temperature is the:
KelvinCelsiusJoule5. 0 °C expressed in kelvin is:
273 K0 K373 K6. Heat is a form of:
EnergyForceMass7. The SI unit of heat energy is the:
JouleNewtonWatt8. Specific heat capacity is the energy to raise ___ of a substance by 1 K.
1 kg1 m³1 litre9. Latent heat is absorbed or released during a:
Change of stateTemperature rise onlyChemical reaction only10. Latent heat of fusion relates to the change between:
Solid and liquidLiquid and gasGas and solid11. Latent heat of vaporisation relates to the change between:
Liquid and gasSolid and liquidSolid and gas12. During a change of state, the temperature:
Stays constantRisesFalls13. Heat transfer through a solid is mainly by:
ConductionConvectionRadiation14. Heat transfer in fluids by bulk movement is:
ConvectionConductionRadiation15. Heat transfer that needs no medium is:
RadiationConductionConvection