First Law of Thermodynamics - UNSOLVED PRACTICE SET
Chapter: Thermodynamics | Topic: First Law of Thermodynamics
FIRST LAW OF THERMODYNAMICS - UNSOLVED PRACTICE SET
Topic: First Law of Thermodynamics
Multiple Choice Questions
Q1. The First Law of Thermodynamics is essentially a statement of:
- Conservation of mass
- Conservation of energy
- Conservation of momentum
- Conservation of charge
Q2. For a cyclic process, the net change in internal energy is:
- Positive
- Negative
- Zero
- Depends on the path
Q3. In an isochoric process, the heat supplied to the system is equal to:
- The work done by the system
- The change in internal energy
- The change in enthalpy
- Zero
Q4. A system absorbs 500 J of heat and does 300 J of work on the surroundings. The change in internal energy is:
- 800 J
- 200 J
- โ200 J
- โ800 J
Q5. For an adiabatic process, the First Law of Thermodynamics reduces to:
- ฮU = q
- ฮU = โw
- ฮU = 0
- ฮU = q + w
Q6. When a gas is compressed adiabatically, its temperature:
- Remains constant
- Decreases
- Increases
- Becomes zero
Short Answer Questions
Q7. State the First Law of Thermodynamics and write its mathematical expression. Explain each term in the equation.
Q8. A system undergoes a cyclic process. Show that the net work done by the system is equal to the net heat absorbed by the system using the First Law.
Q9. Explain why the First Law of Thermodynamics does not tell us anything about the direction of a spontaneous process.
Q10. In an isothermal expansion of an ideal gas, why is ฮU = 0? Use the First Law to explain what happens to the heat absorbed.
Q11. A student performs an experiment where 2 moles of an ideal gas are heated at constant volume. Using the First Law, explain what happens to the heat supplied.
Q12. Why can't we build a perpetual motion machine of the first kind? Explain with reference to the First Law of Thermodynamics.
Long Answer Questions
Q13. (a) State and explain the First Law of Thermodynamics with a suitable example.
(b) Show that for an ideal gas undergoing an isothermal process, q = โw.
(c) A student claims that it is possible to create a machine that produces work continuously without any energy input. Use the First Law to explain why this is impossible.
Q14. (a) Apply the First Law of Thermodynamics to derive the relationship between Cp and Cv for an ideal gas.
(b) Explain the physical significance of the difference Cp โ Cv = R.
(c) For a monoatomic ideal gas, show that Cp = (5/2)R and Cv = (3/2)R using the First Law.
Q15. (a) Describe an experiment to verify the First Law of Thermodynamics.
(b) A gas is taken from state A to state B by two different paths โ one reversible and one irreversible. Compare ฮU, q, and w for both paths. What does this tell you about the nature of these quantities?
Numerical / Application-Based Problems
Q16. A system absorbs 650 J of heat and does 420 J of work on the surroundings.
(a) Calculate the change in internal energy of the system.
(b) If the system now returns to its original state by a different path, absorbing 300 J of heat, how much work is done on or by the system?
Q17. One mole of an ideal monoatomic gas is heated from 300 K to 500 K.
(a) Calculate the change in internal energy (ฮU).
(b) Calculate the heat absorbed (q) if the heating is done at constant volume.
(c) Calculate the heat absorbed (q) if the heating is done at constant pressure.
(d) Calculate the work done in the constant pressure process.
(Given: Cv = (3/2)R, Cp = (5/2)R, R = 8.314 J/molยทK)
Q18. In a school science project, a student designs a simple heat engine that absorbs 1000 J of heat from a hot reservoir, does 600 J of work, and rejects the remaining heat to a cold reservoir.
(a) Calculate the heat rejected to the cold reservoir using the First Law.
(b) The student claims that by improving the design, the engine can produce 1000 J of work from 1000 J of heat. Is this claim valid? Explain using the First Law.
(c) Calculate the efficiency of the engine described in part (a).