EIT Thermodynamics 2 — Questions and Answers
Question 1: 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?
- 37.5%
- 62.5% (Correct answer)
- 27.5%
- 72.5%
Correct answer: 62.5%
Carnot efficiency = 1 - T_cold/T_hot = 1 - 300/800 = 0.625 = 62.5%.
Question 2: Which thermodynamic process occurs at constant pressure?
- Isochoric
- Isobaric (Correct answer)
- Isothermal
- Isentropic
Correct answer: Isobaric
An isobaric process occurs at constant pressure, unlike isochoric (constant volume) or isothermal (constant temperature).
Question 3: For an ideal gas undergoing an isentropic (adiabatic reversible) process, which relationship is correct (k = Cp/Cv)?
- PV = constant
- TV^(k-1) = constant
- PV^k = constant
- Both B and C (Correct answer)
Correct answer: Both B and C
Both TV^(k-1) = constant and PV^k = constant hold for an isentropic process with an ideal gas.
Question 4: The Clausius inequality states that for any cycle, ∮(δQ/T) is:
- Always positive
- Equal to zero only for reversible cycles and negative for irreversible cycles (Correct answer)
- Always negative
- Always equal to zero
Correct 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.
Question 5: 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?
- Enthalpy
- Entropy (Correct answer)
- Temperature
- Internal energy
Correct answer: Entropy
An isentropic (reversible adiabatic) process maintains constant entropy.
Question 6: 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)?
- 0.4
- 2.5 (Correct answer)
- 3.5
- 1.5
Correct answer: 2.5
COP_refrigerator = Q_L / W_net = 500 / 200 = 2.5.
Question 7: 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?
- 0
- 1 (Correct answer)
- 2
- 3
Correct answer: 1
F = 1 - 2 + 2 = 1; only one intensive variable (e.g., temperature or pressure) can be independently varied.
EIT Thermodynamics 2
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?