First law of thermodynamics work heat internal energy and enthalpy - Question Bank

1. The enthalpy of a system is defined as:
A) The sum of its internal energy and the product of its pressure and volume.
B) The heat transferred at constant volume.
C) The work done by the system.
D) The absolute temperature multiplied by entropy.
2. Which of the following scenarios would result in zero change in internal energy (ΔU = 0)?
A) A system absorbs heat and does work equal to the heat absorbed.
B) A system releases heat and work is done on it.
C) An adiabatic process where work is done on the system.
D) A process at constant volume with heat absorbed.
3. For a reaction where the number of moles of gaseous products is less than the number of moles of gaseous reactants (Δn_gas < 0), which relationship holds true?
A) ΔH > ΔU
B) ΔH < ΔU
C) ΔH = ΔU
D) ΔH = ΔU - RT
4. For a reaction where the number of moles of gaseous products is greater than the number of moles of gaseous reactants (Δn_gas > 0), which relationship holds true?
A) ΔH < ΔU
B) ΔH > ΔU
C) ΔH = ΔU
D) ΔH = ΔU + RT
5. Work done during reversible isothermal expansion of an ideal gas is given by:
A) -nRT log(V₂/V₁)
B) -nRT log(P₂/P₁)
C) PΔV
D) nRT
6. If 500 calories of heat are supplied to a system, and the system does 1000 J of work, what is the change in internal energy (1 cal = 4.184 J)?
A) 2092 J
B) 1092 J
C) -1092 J
D) 3092 J
7. An isolated system can exchange with its surroundings:
A) Only energy
B) Only matter
C) Both energy and matter
D) Neither energy nor matter
8. A closed system can exchange with its surroundings:
A) Only energy
B) Only matter
C) Both energy and matter
D) Neither energy nor matter
9. An open system can exchange with its surroundings:
A) Only energy
B) Only matter
C) Both energy and matter
D) Neither energy nor matter
10. What defines the boundary between a system and its surroundings?
A) It must be permeable
B) It must be rigid
C) It is the interface separating the system from its surroundings
D) It must be insulating
11. What does the term 'system' refer to in thermodynamics?
A) The universe excluding the surroundings
B) A specific part of the universe under study
C) Everything outside the boundary of the study
D) The boundary itself
12. Consider the reaction: N₂(g) + 3H₂(g) → 2NH₃(g). For this reaction, ΔH is related to ΔU by:
A) ΔH = ΔU
B) ΔH = ΔU - 2RT
C) ΔH = ΔU + 2RT
D) ΔH = ΔU + RT
13. What is the definition of enthalpy?
A) The total energy of a system
B) The heat content of a system
C) The energy of a system plus the product of its pressure and volume
D) The energy transferred as heat
14. When is ΔH equal to ΔU?
A) At constant pressure and constant volume
B) At constant temperature
C) When there is no change in the number of moles of gas
D) During an adiabatic process
15. A system releases 80 J of heat and its internal energy increases by 40 J. How much work was done?
A) 40 J
B) -40 J
C) 120 J
D) -120 J
16. Which of the following is NOT a unit of energy or work?
A) Joule
B) Calorie
C) Pascal
D) Erg
17. If a system undergoes a cycle, returning to its initial state, what is the change in internal energy (ΔU) and enthalpy (ΔH)?
A) ΔU ≠ 0, ΔH ≠ 0
B) ΔU = 0, ΔH ≠ 0
C) ΔU ≠ 0, ΔH = 0
D) ΔU = 0, ΔH = 0
18. For an adiabatic process, the First Law of Thermodynamics simplifies to:
A) ΔU = q
B) ΔU = w
C) ΔU = 0
D) ΔH = 0
19. In an adiabatic process, what is the heat transfer (q)?
A) Zero
B) Positive
C) Negative
D) Equal to ΔH
20. What is the internal energy change for a process where ΔH = 50 kJ and PΔV = -15 kJ?
A) 65 kJ
B) 35 kJ
C) 50 kJ
D) -15 kJ
21. What is the enthalpy change for a process where ΔU = 100 kJ and PΔV = 30 kJ?
A) 70 kJ
B) 130 kJ
C) 100 kJ
D) 30 kJ
22. Which of the following expressions correctly represents the work done by a gas during expansion against a constant external pressure?
A) w = -PΔV
B) w = PΔV
C) w = -ΔV/P
D) w = ΔV
23. If ΔU is positive, it means the internal energy of the system has:
A) Decreased
B) Increased
C) Remained the same
D) Become zero
24. For an ideal gas, the internal energy (U) depends only on:
A) Pressure
B) Volume
C) Temperature
D) Number of moles
25. Internal energy (U) is a function of:
A) Temperature and Pressure only
B) Temperature only
C) Pressure and Volume only
D) Temperature and Volume only
26. Which thermodynamic law is also known as the law of conservation of energy?
A) Zeroth Law
B) First Law
C) Second Law
D) Third Law
27. If a process occurs at constant temperature and pressure, and the system expands, what is the sign of work?
A) Positive
B) Negative
C) Zero
D) Cannot be determined
28. What is the sign of work done ON the system during compression?
A) Positive
B) Negative
C) Zero
D) Cannot be determined
29. What is the sign of work done BY the system during expansion?
A) Positive
B) Negative
C) Zero
D) Cannot be determined
30. For a free expansion of an ideal gas, ΔU is:
A) Positive
B) Negative
C) Zero
D) Dependent on pressure
31. In the expansion of an ideal gas into a vacuum (free expansion), what are the values of heat (q) and work (w)?
A) q = 0, w ≠ 0
B) q ≠ 0, w = 0
C) q = 0, w = 0
D) q ≠ 0, w ≠ 0
32. What is the relationship between internal energy (U), enthalpy (H), pressure (P), and volume (V)?
A) H = U - PV
B) U = H + PV
C) H = U + PV
D) PV = U + H
33. If a chemical reaction has ΔH > 0, it is:
A) Exothermic and releases heat
B) Endothermic and absorbs heat
C) An isochoric process
D) A process with no heat transfer
34. If a chemical reaction has ΔH < 0, it is:
A) Endothermic and absorbs heat
B) Exothermic and releases heat
C) Neither endothermic nor exothermic
D) An isobaric process
35. Consider a system where 200 J of work is done BY the system, and it absorbs 150 J of heat. What is the change in internal energy?
A) 350 J
B) 50 J
C) -50 J
D) -350 J
36. When is enthalpy change (ΔH) equal to the heat absorbed or released?
A) At constant volume
B) At constant temperature
C) At constant pressure
D) During adiabatic processes
37. Which of the following is NOT a state function?
A) Enthalpy
B) Internal Energy
C) Heat
D) Entropy
38. Which of the following is a state function in thermodynamics?
A) Heat
B) Work
C) Internal Energy
D) Path
39. If ΔU = 0 for a process, what can be concluded about the heat and work exchanged?
A) q = w
B) q = -w
C) q = 0
D) w = 0
40. For an isochoric process (constant volume), the work done (w) is:
A) Zero
B) Positive
C) Negative
D) Equal to ΔH
41. If a system releases 100 J of heat and 30 J of work is done on the system, what is the change in internal energy (ΔU)?
A) -130 J
B) -70 J
C) 70 J
D) 130 J
42. If a system absorbs 50 J of heat and does 20 J of work on the surroundings, what is the change in internal energy (ΔU)?
A) 70 J
B) 30 J
C) -30 J
D) -70 J
43. In the equation ΔH = ΔU + PΔV, what does PΔV represent?
A) Work done by the system at constant volume
B) Heat absorbed at constant pressure
C) Work done by the system at constant pressure
D) Change in internal energy
44. For an endothermic process occurring at constant pressure, what is the sign of ΔH?
A) Negative
B) Positive
C) Zero
D) Cannot be determined
45. For an exothermic process occurring at constant pressure, what is the sign of ΔH?
A) Positive
B) Negative
C) Zero
D) Cannot be determined
46. Which thermodynamic quantity is defined as the heat absorbed or released by a system at constant pressure?
A) Internal Energy
B) Heat
C) Work
D) Enthalpy
47. The change in internal energy (ΔU) of a system is dependent on:
A) The path taken between initial and final states
B) The initial and final states only
C) The amount of heat transferred only
D) The amount of work done only
48. What does 'w' represent in the First Law of Thermodynamics equation, ΔU = q + w, when work is done ON the system?
A) Work done by the system
B) Heat absorbed by the system
C) Work done on the system
D) Enthalpy change
49. What does 'q' represent in the First Law of Thermodynamics equation, ΔU = q + w?
A) Work done by the system
B) Heat absorbed by the system
C) Change in internal energy
D) Enthalpy change
50. In thermodynamic terms, what is defined as the energy transferred between a system and its surroundings due to a temperature difference?
A) Work
B) Internal Energy
C) Enthalpy
D) Heat
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