THERMODYNAMICS 2026 – VERIFIED
PRACTICE QUESTIONS, ENERGY SYSTEMS &
HEAT TRANSFER EXAM PREP
QUESTION 1 Which of the following best describes the First Law of Thermodynamics?
• A) Energy cannot be created but can be destroyed
• B) Energy cannot be created or destroyed, only transferred or converted
• C) Heat always flows from cold to hot
• D) Entropy of the universe always decreases
RATIONALE: The First Law is the law of conservation of energy. It states that the total energy
of an isolated system remains constant — energy is neither created nor destroyed, only
transformed from one form to another.
QUESTION 2 A system undergoes a process where no heat is exchanged with the surroundings.
This process is called:
• A) Isothermal
• B) Isobaric
• C) Adiabatic
• D) Isochoric
RATIONALE: An adiabatic process is one in which no heat transfer (Q = 0) occurs between
the system and its surroundings. The temperature may still change due to work done.
QUESTION 3 The efficiency of a Carnot engine operating between temperatures T_H = 600 K
and T_L = 300 K is:
• A) 25%
• B) 75%
• C) 50%
• D) 100%
RATIONALE: Carnot efficiency η = 1 – (T_L/T_H) = 1 – (300/600) = 1 – 0.5 = 0.50 = 50%.
,QUESTION 4 Which thermodynamic property is defined as U + PV?
• A) Entropy
• B) Gibbs free energy
• C) Helmholtz energy
• D) Enthalpy
RATIONALE: Enthalpy H is defined as H = U + PV, where U is internal energy, P is pressure,
and V is volume. It is particularly useful in constant-pressure processes.
QUESTION 5 The Second Law of Thermodynamics states that:
• A) Energy is conserved in all processes
• B) Work can be fully converted to heat
• C) The entropy of an isolated system always increases or remains constant
• D) All processes are reversible
RATIONALE: The Second Law establishes the direction of thermodynamic processes. For an
isolated system, entropy (disorder) never decreases — it either increases (irreversible) or stays
the same (reversible).
QUESTION 6 In a throttling process (e.g., a valve), which quantity remains constant?
• A) Temperature
• B) Pressure
• C) Entropy
• D) Enthalpy
RATIONALE: In a throttling (isenthalpic) process, there is no work done and no heat transfer,
so enthalpy remains constant: h₁ = h₂. Pressure drops but enthalpy is conserved.
QUESTION 7 Which of the following is an intensive property?
• A) Volume
, • B) Mass
• C) Temperature
• D) Internal energy
RATIONALE: Intensive properties do not depend on the amount of matter in a system.
Temperature, pressure, and density are intensive. Volume, mass, and internal energy are
extensive.
QUESTION 8 For an ideal gas undergoing an isothermal process, which of the following is
TRUE?
• A) Internal energy increases
• B) Internal energy remains constant
• C) Pressure remains constant
• D) Volume remains constant
RATIONALE: For an ideal gas, internal energy depends only on temperature. In an isothermal
process, temperature is constant, so ΔU = 0. Work done equals heat added: Q = W.
QUESTION 9 The Clausius inequality states that for any cycle:
• A) ∮ dQ/T > 0
• B) ∮ dQ/T = 1
• C) ∮ dQ/T ≤ 0
• D) ∮ dQ/T ≥ 1
RATIONALE: The Clausius inequality states ∮ δQ/T ≤ 0. The equality holds for reversible
cycles, and the inequality for irreversible ones. This is a mathematical expression of the Second
Law.
QUESTION 10 Heat transfer that occurs through electromagnetic waves and requires no
medium is called:
• A) Conduction
, • B) Convection
• C) Radiation
• D) Advection
RATIONALE: Radiation is the transfer of heat via electromagnetic waves (infrared). Unlike
conduction and convection, it does not require a material medium and can occur through a
vacuum.
QUESTION 11 What is the thermal efficiency of a heat engine that receives 1000 kJ of heat and
rejects 600 kJ?
• A) 60%
• B) 40%
• C) 30%
• D) 50%
RATIONALE: η = W_net/Q_H = (Q_H – Q_L)/Q_H = (1000 – 600)/1000 = 400/1000 = 40%.
QUESTION 12 Which of the following processes occurs at constant volume?
• A) Isobaric
• B) Isothermal
• C) Adiabatic
• D) Isochoric
RATIONALE: An isochoric (also called isovolumetric) process occurs at constant volume.
Since dV = 0, no boundary work is done (W = 0), and all heat added goes directly to changing
internal energy.
QUESTION 13 Fourier's Law of heat conduction states:
• A) Q = mCΔT
• B) Q̇ = –kA(dT/dx)
• C) Q = σAT⁴
PRACTICE QUESTIONS, ENERGY SYSTEMS &
HEAT TRANSFER EXAM PREP
QUESTION 1 Which of the following best describes the First Law of Thermodynamics?
• A) Energy cannot be created but can be destroyed
• B) Energy cannot be created or destroyed, only transferred or converted
• C) Heat always flows from cold to hot
• D) Entropy of the universe always decreases
RATIONALE: The First Law is the law of conservation of energy. It states that the total energy
of an isolated system remains constant — energy is neither created nor destroyed, only
transformed from one form to another.
QUESTION 2 A system undergoes a process where no heat is exchanged with the surroundings.
This process is called:
• A) Isothermal
• B) Isobaric
• C) Adiabatic
• D) Isochoric
RATIONALE: An adiabatic process is one in which no heat transfer (Q = 0) occurs between
the system and its surroundings. The temperature may still change due to work done.
QUESTION 3 The efficiency of a Carnot engine operating between temperatures T_H = 600 K
and T_L = 300 K is:
• A) 25%
• B) 75%
• C) 50%
• D) 100%
RATIONALE: Carnot efficiency η = 1 – (T_L/T_H) = 1 – (300/600) = 1 – 0.5 = 0.50 = 50%.
,QUESTION 4 Which thermodynamic property is defined as U + PV?
• A) Entropy
• B) Gibbs free energy
• C) Helmholtz energy
• D) Enthalpy
RATIONALE: Enthalpy H is defined as H = U + PV, where U is internal energy, P is pressure,
and V is volume. It is particularly useful in constant-pressure processes.
QUESTION 5 The Second Law of Thermodynamics states that:
• A) Energy is conserved in all processes
• B) Work can be fully converted to heat
• C) The entropy of an isolated system always increases or remains constant
• D) All processes are reversible
RATIONALE: The Second Law establishes the direction of thermodynamic processes. For an
isolated system, entropy (disorder) never decreases — it either increases (irreversible) or stays
the same (reversible).
QUESTION 6 In a throttling process (e.g., a valve), which quantity remains constant?
• A) Temperature
• B) Pressure
• C) Entropy
• D) Enthalpy
RATIONALE: In a throttling (isenthalpic) process, there is no work done and no heat transfer,
so enthalpy remains constant: h₁ = h₂. Pressure drops but enthalpy is conserved.
QUESTION 7 Which of the following is an intensive property?
• A) Volume
, • B) Mass
• C) Temperature
• D) Internal energy
RATIONALE: Intensive properties do not depend on the amount of matter in a system.
Temperature, pressure, and density are intensive. Volume, mass, and internal energy are
extensive.
QUESTION 8 For an ideal gas undergoing an isothermal process, which of the following is
TRUE?
• A) Internal energy increases
• B) Internal energy remains constant
• C) Pressure remains constant
• D) Volume remains constant
RATIONALE: For an ideal gas, internal energy depends only on temperature. In an isothermal
process, temperature is constant, so ΔU = 0. Work done equals heat added: Q = W.
QUESTION 9 The Clausius inequality states that for any cycle:
• A) ∮ dQ/T > 0
• B) ∮ dQ/T = 1
• C) ∮ dQ/T ≤ 0
• D) ∮ dQ/T ≥ 1
RATIONALE: The Clausius inequality states ∮ δQ/T ≤ 0. The equality holds for reversible
cycles, and the inequality for irreversible ones. This is a mathematical expression of the Second
Law.
QUESTION 10 Heat transfer that occurs through electromagnetic waves and requires no
medium is called:
• A) Conduction
, • B) Convection
• C) Radiation
• D) Advection
RATIONALE: Radiation is the transfer of heat via electromagnetic waves (infrared). Unlike
conduction and convection, it does not require a material medium and can occur through a
vacuum.
QUESTION 11 What is the thermal efficiency of a heat engine that receives 1000 kJ of heat and
rejects 600 kJ?
• A) 60%
• B) 40%
• C) 30%
• D) 50%
RATIONALE: η = W_net/Q_H = (Q_H – Q_L)/Q_H = (1000 – 600)/1000 = 400/1000 = 40%.
QUESTION 12 Which of the following processes occurs at constant volume?
• A) Isobaric
• B) Isothermal
• C) Adiabatic
• D) Isochoric
RATIONALE: An isochoric (also called isovolumetric) process occurs at constant volume.
Since dV = 0, no boundary work is done (W = 0), and all heat added goes directly to changing
internal energy.
QUESTION 13 Fourier's Law of heat conduction states:
• A) Q = mCΔT
• B) Q̇ = –kA(dT/dx)
• C) Q = σAT⁴
