Thermodynamics and Entropy Flashcards

Grade 12 · Science · Flashcards

Key thermodynamics vocabulary and laws for Grade 12 Science.

Flashcards

Zeroth Law of Thermodynamics: If A is in thermal equilibrium with C and B is in thermal equilibrium with C, then A and B are in thermal equilibrium with each other.
First Law of Thermodynamics: Energy is conserved: ΔU = Q − W (internal energy change = heat added − work done by system).
Second Law of Thermodynamics: Entropy of the universe increases in all spontaneous processes; heat flows naturally from hot to cold.
Third Law of Thermodynamics: The entropy of a perfect crystal at absolute zero (0 K) is zero.
Entropy (S): A thermodynamic state function measuring disorder; ΔS > 0 for spontaneous isolated processes.
Enthalpy (H): Heat content at constant pressure; ΔH = Hproducts − Hreactants; negative for exothermic.
Gibbs Free Energy (G): G = H − TS; ΔG < 0 = spontaneous, ΔG = 0 = equilibrium, ΔG > 0 = non-spontaneous.
Exothermic reaction: Releases heat to surroundings; ΔH < 0; example: combustion.
Endothermic reaction: Absorbs heat from surroundings; ΔH > 0; example: melting ice.
Carnot efficiency: Maximum theoretical efficiency of a heat engine: η = 1 − Tc/Th, where Tc and Th are cold and hot reservoir temperatures in Kelvin.
Heat (Q): Energy transferred between systems due to temperature difference; measured in joules.
Absolute zero: 0 Kelvin = −273.15°C; theoretical temperature at which all molecular motion ceases.