Thermodynamics Flashcards

A Carnot heat engine operates between a hot reservoir at 800 K and a cold reservoir at 300 K. What is its maximum thermal efficiency?

Answer: 62.5%

Carnot efficiency = 1 - T_cold/T_hot = 1 - 300/800 = 0.625 = 62.5%.

Which thermodynamic process occurs at constant pressure?

Answer: Isobaric

An isobaric process occurs at constant pressure, unlike isochoric (constant volume) or isothermal (constant temperature).

For an ideal gas undergoing an isentropic (adiabatic reversible) process, which relationship is correct (k = Cp/Cv)?

Answer: Both B and C

Both TV^(k-1) = constant and PV^k = constant hold for an isentropic process with an ideal gas.

The Clausius inequality states that for any cycle, ∮(δQ/T) is:

Answer: Equal to zero only for reversible cycles and negative for irreversible cycles

The Clausius inequality: ∮(δQ/T) ≤ 0, where equality holds for reversible cycles and strict inequality for irreversible cycles.

Steam enters a turbine at 3 MPa and 350°C and exits at 100 kPa. Assuming isentropic expansion, which property remains constant through the turbine?

Answer: Entropy

An isentropic (reversible adiabatic) process maintains constant entropy.

A refrigerator removes 500 kJ of heat from a cold space and requires 200 kJ of work input. What is its coefficient of performance (COP)?

Answer: 2.5

COP_refrigerator = Q_L / W_net = 500 / 200 = 2.5.

The Gibbs phase rule for a non-reacting system is F = C - P + 2. For a pure substance (C=1) in a two-phase region (P=2), how many degrees of freedom exist?

Answer: 1

F = 1 - 2 + 2 = 1; only one intensive variable (e.g., temperature or pressure) can be independently varied.