Skip to main content
ExamWize
Sign up

FE · 10% of the exam

Thermodynamics practice questions

10 free Thermodynamics questions for the FE Mechanical Exam (FE) exam, each with the correct answer and an explanation for every option.

Start the questionsFree 10-question FE quiz

What this domain covers

One of the four largest domains: properties of substances, the laws of thermodynamics, cycles, psychrometrics and combustion.

Exam weight
10%
On a real exam
≈ 11 questions
In our bank
60 questions

Topics that come up most

  • Steam tables and ideal gas properties
  • First and second law for open and closed systems
  • Rankine, Brayton and refrigeration cycles
  • Psychrometrics and HVAC processes
  • Combustion and air-fuel ratios

How to study it

Get fluent at finding states in the steam and refrigerant tables, including interpolation and quality; most cycle questions depend on it.

Sample Thermodynamics questions

Try each one before opening the answer. Original questions written to the official exam objectives.

  1. Question 1

    For air treated as an ideal gas, cp = 1.005 kJ/kg·K and R = 0.287 kJ/kg·K. Its cv is:

    • A3.50 kJ/kg·K
    • B1.292 kJ/kg·K
    • C0.718 kJ/kg·K
    • D0.288 kJ/kg·K
    Show answer and explanation

    Answer: C) 0.718 kJ/kg·K

    • AIncorrect. Recheck the relationship.
    • BIncorrect. Subtract R, don't add.
    • CCorrect. \(c_v = c_p - R\).
    • DIncorrect. Recheck the relationship.

  2. Question 2

    For any real (irreversible) process, total entropy generation is:

    • ALess than zero
    • BGreater than zero
    • CExactly zero
    • DUndefined
    Show answer and explanation

    Answer: B) Greater than zero

    • AIncorrect. That violates the second law.
    • BCorrect. It's zero only for reversible processes.
    • CIncorrect. That's only for reversible processes.
    • DIncorrect. It's positive.

  3. Question 3

    The quality x of a saturated liquid-vapor mixture is the:

    • AMass fraction that is vapor
    • BMass fraction that is liquid
    • CVolume fraction of liquid
    • DTemperature ratio
    Show answer and explanation

    Answer: A) Mass fraction that is vapor

    • ACorrect. x = m_vapor/m_total.
    • BIncorrect. That's 1 − x.
    • CIncorrect. It's the vapor mass fraction.
    • DIncorrect. It's the vapor mass fraction.

  4. Question 4

    A 1-m³ tank holds air (R = 0.287 kJ/kg·K) at 500 kPa and 500 K. The mass of air is about:

    • A1.74 kg
    • B0.29 kg
    • C3.48 kg
    • D348 kg
    Show answer and explanation

    Answer: C) 3.48 kg

    • AIncorrect. Recheck the calculation.
    • BIncorrect. Recheck the formula.
    • CCorrect. \(m = PV/(RT) = 500/(0.287 \times 500)\).
    • DIncorrect. Recheck the units.

  5. Question 5

    A refrigerator removes 5 kW from its cold space using 1.25 kW of work. Its coefficient of performance is:

    • A5
    • B4
    • C0.25
    • D6.25
    Show answer and explanation

    Answer: B) 4

    • AIncorrect. That's the heat pump COP (Q_H/W).
    • BCorrect. COP = Q_L/W.
    • CIncorrect. That's inverted.
    • DIncorrect. Divide, don't add.

  6. Question 6

    A turbine produces 800 kJ/kg; the isentropic process between the same states would produce 1,000 kJ/kg. Its isentropic efficiency is:

    • A20%
    • B125%
    • C80%
    • D90%
    Show answer and explanation

    Answer: C) 80%

    • AIncorrect. That's the loss fraction.
    • BIncorrect. That's inverted.
    • CCorrect. For turbines, actual/isentropic work.
    • DIncorrect. Recheck the ratio.

  7. Question 7

    A Rankine cycle produces 900 kJ/kg of net work with 2,700 kJ/kg of heat added in the boiler. Its thermal efficiency is about:

    • A33%
    • B50%
    • C67%
    • D25%
    Show answer and explanation

    Answer: A) 33%

    Thermal efficiency is net work divided by heat added: η = 900/2,700 ≈ 33%.

    • ACorrect. Thermal efficiency = net work ÷ heat added = 900/2,700 ≈ 0.33, or 33%.
    • BIncorrect. This divides net work by the heat rejected (2,700 − 900 = 1,800 kJ/kg). Efficiency uses the heat added, not the heat rejected.
    • CIncorrect. This is the fraction of the added heat that is rejected (1,800/2,700), not the fraction turned into net work.
    • DIncorrect. This divides net work by the sum of heat added and net work (900/3,600). The denominator should be the heat added alone.

  8. Question 8

    An ideal compressor raises the temperature of 1 kg/s of air (cp = 1.005 kJ/kg·K) by 200 K, adiabatically. The power required is about:

    • A201 kW
    • B144 kW, using cv
    • C20.1 kW
    • D402 kW
    Show answer and explanation

    Answer: A) 201 kW

    • ACorrect. \(\dot{W} = \dot{m}c_p\Delta T\).
    • BIncorrect. Steady flow uses cp.
    • CIncorrect. That's off by a factor of 10.
    • DIncorrect. That doubles the result.

  9. Question 9

    A Carnot refrigerator operates between 270 K and 300 K. Its coefficient of performance is:

    • A0.9
    • B10
    • C9
    • D1.11
    Show answer and explanation

    Answer: C) 9

    • AIncorrect. That's \(T_L/T_H\).
    • BIncorrect. That's the Carnot heat pump COP.
    • CCorrect. \(T_L/(T_H - T_L) = 270/30\).
    • DIncorrect. Recheck the formula.

  10. Question 10

    In an ideal Rankine cycle, water (v ≈ 0.001 m³/kg) is pumped through a 3,000-kPa pressure rise. The pump work is about:

    • A30 kJ/kg
    • B3,000 kJ/kg, omitting the specific volume
    • C0.3 kJ/kg
    • D3 kJ/kg
    Show answer and explanation

    Answer: D) 3 kJ/kg

    • AIncorrect. That's off by a factor of 10.
    • BIncorrect. Multiply by v.
    • CIncorrect. That's off by a factor of 10.
    • DCorrect. \(w = v\Delta P\).

Thermodynamics: FAQs

How much of the FE exam is Thermodynamics?

Thermodynamics is 10% of the FE exam by the official exam guide's weighting, which on a 110-question form works out to roughly 11 questions. The real exam's exact split varies by form.

What does the Thermodynamics domain cover?

One of the four largest domains: properties of substances, the laws of thermodynamics, cycles, psychrometrics and combustion.

How should I study Thermodynamics for FE?

Get fluent at finding states in the steam and refrigerant tables, including interpolation and quality; most cycle questions depend on it.

Where can I practise more Thermodynamics questions?

This page has 10 free Thermodynamics questions with answers. The ExamWize FE question bank has 60 questions in this domain. Every practice exam result breaks your score down by domain, and Review Mode re-drills the questions you missed.

Other FE topics

Also: 15 free questions across all topics, the FE cheat sheet and the study guide.

Get Thermodynamics exam-ready

The full FE bank has 60 Thermodynamics questions. Timed practice exams match the real exam's length and domain weights, every result shows your score per domain, and Review Mode re-drills the questions you missed.

See the full FE practice examsTake the free diagnostic

Not affiliated with NCEES; questions are original, written from the official exam outline, and never copied from the real exam.