Kelvin–Planck and Clausius, engine efficiency and the Carnot ceiling η = 1 − T₂/T₁, petrol against diesel stroke by stroke, the coefficient of performance of a fridge, and entropy as ΔS = Q/T.
Unit 2 carries 7 of the 50 physics marks; with six chapters sharing them, this one averages a little over one (MEC publishes weights by unit, not by chapter). It closes the unit and it is the most quotable chapter in it: two statements, two formulae and one comparison table carry almost every question that can be set.
The MEC scope lines are: Heat engines (internal combustion) and refrigerators; Concept of entropy. The headings below are those two points, in MEC's order.
Three ways it is asked: recall (the Kelvin–Planck and Clausius statements, the four strokes of a petrol engine, the unit of entropy); understanding (why no engine can be 100 % efficient, why lowering the sink temperature helps more than raising the source, why a coefficient of performance may exceed 1, why leaving the refrigerator door open warms the kitchen); application (a Carnot efficiency, a source temperature from a given efficiency, the heat rejected per cycle, a coefficient of performance, an entropy change on melting).
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See the plansHeat, Temperature and Thermometers: What Each One Can Read
Heat against temperature against internal energy, the scales and the −40 coincidence, the zeroth law, conduction, convection and radiation, and the three thermometers MEC names side by side.
Heat and Thermodynamics: Unit Map and Reading Order
What the Heat and thermodynamics unit covers, how many of the 50 Physics questions it carries, and the order to read its six chapter notes in.
Thermal Expansion: One Coefficient, Three Dimensions
Why α : β : γ is 1 : 2 : 3, how a hole and a bimetallic strip behave, why a pendulum clock loses time in summer, and the real-against-apparent expansion of a liquid in its vessel.
Quantity of Heat: Mixtures, Latent Heat and the Triple Point
Heat capacity against specific heat capacity, the method of mixtures done cleanly, latent heats and the heating curve read properly, evaporation against boiling, and the triple point of water.