Heat and Thermodynamics
What this domain tests
Heat and Thermodynamics tests thermal expansion, calorimetry, heat transfer, the first law, thermodynamic processes and Carnot efficiency.
Core rules
- Linear expansion ΔL = αLΔT; area and volume expansions use 2α and 3α for isotropic solids.
- Heat gained or lost Q = mcΔT; during a phase change Q = mL with no temperature change.
- First law: ΔU = Q − W, where W is work done by the gas.
- Isothermal: ΔU = 0, W = nRT ln(V₂/V₁). Adiabatic: Q = 0, TV^{γ−1} = constant.
- Carnot efficiency η = 1 − T₂/T₁, with temperatures in kelvin.
Worked example
A gas absorbs 500 J of heat and does 200 J of work on its surroundings. By the first law, ΔU = Q − W = 500 − 200 = 300 J. The internal energy rises by 300 J. If the gas had been compressed so that 200 J of work was done on it, W = −200 J and ΔU would be 700 J.
Traps
Using Celsius temperatures in Carnot efficiency; reversing the sign of W in the first law; assuming ΔU = 0 in an adiabatic process; forgetting latent heat during melting or boiling; treating conduction, convection and radiation as interchangeable in numerical problems.