Thermodynamics for Engineers 2026 Solved Problems

1. What does the First Law of Thermodynamics state regarding a closed system? A) Entropy always increases in an isolated system. B) The change in internal energy is equal to the heat added to the system minus the work done by the system ($Delta U = Q - W$). C) Absolute zero cannot be reached. D) Energy can be created from nothing. Correct Answer: B) The change in internal energy is equal to the heat added to the system minus the work done by the system ($Delta U = Q - W$). 2. An ideal gas undergoes an adiabatic process. What is the value of heat transfer ($Q$)? A) $Q 0$ B) $Q 0$ C) $Q = 0$ D) $Q = Delta U$ Correct Answer: C) $Q = 0$ 3. In a reversible Carnot cycle, what determines the efficiency ($eta$)? A) The working substance used B) The temperatures of the hot ($T _ H$) and cold ($T _ C$) reservoirs: $eta = 1 - (T C / T _ _ C) The pressure of the gas D) The volume of the cylinder H)$ Correct Answer: B) The temperatures of the hot ($T _ H$) and cold ($T _ C$) reservoirs: $eta = 1 - (T C / T _ _ H)$ 4. What is the definition of "Entropy" in the Second Law of Thermodynamics? A) A measure of energy potential B) A measure of the disorder or randomness of a system C) The total heat capacity of a substance D) The work done by a machine Correct Answer: B) A measure of the disorder or randomness of a system 5. For an isolated system, the Second Law of Thermodynamics dictates that: A) $Delta S 0$ B) $Delta S = 0$ C) $Delta S ge 0$ D) $Delta S = Delta H$ Correct Answer: C) $Delta S ge 0$ 6. What is the enthalpy ($H$) of a system defined as? A) $H = U + PV$ B) $H = U - PV$ C) $H = Q / T$ D) $H = Delta U + W$ Correct Answer: A) $H = U + PV$ 7. In an isobaric process, which parameter remains constant? A) Temperature B) Pressure C) Volume D) Entropy Correct Answer: B) Pressure 8. What is the relationship between Gibbs Free Energy ($Delta G$), Enthalpy ($Delta H$), and Entropy ($Delta S$)? A) $Delta G = Delta H + TDelta S$ B) $Delta G = Delta H - TDelta S$ C) $Delta G = Delta S - TDelta H$ D) $Delta G = T(Delta H - Delta S)$ Correct Answer: B) $Delta G = Delta H - TDelta S$ 9. A process is considered spontaneous when: A) $Delta G 0$ B) $Delta G = 0$ C) $Delta G 0$ D) $Delta H = 0$ Correct Answer: C) $Delta G 0$ 10. What is the "Quality" of steam ($x$)? A) The temperature of the steam B) The mass fraction of vapor in a liquid-vapor mixture C) The pressure of the steam D) The enthalpy of the steam Correct Answer: B) The mass fraction of vapor in a liquid-vapor mixture 11. In the Otto cycle (gasoline engine), what process occurs during the power stroke? A) Adiabatic compression B) Isochoric heat addition C) Adiabatic expansion D) Isobaric heat rejection Correct Answer: C) Adiabatic expansion