Based on the first law of thermodynamics, which one of the following is correct?(a) For an isothermal irreversible change , q = +w(b) For an isochoric process, ΔU = -q(c) For an adiabatic process, ΔU = -w(d) For isothermal irreversible change , q = -w
Question
Based on the first law of thermodynamics, which one of the following is correct?(a) For an isothermal irreversible change , q = +w(b) For an isochoric process, ΔU = -q(c) For an adiabatic process, ΔU = -w(d) For isothermal irreversible change , q = -w
Solution
Based on the first law of thermodynamics, let's analyze each option step by step:
(a) For an isothermal irreversible change, q = +w:
- Isothermal means that the temperature remains constant during the process.
- Irreversible means that the process cannot be reversed without external intervention.
- According to the first law of thermodynamics, the change in internal energy (ΔU) is equal to the heat transfer (q) minus the work done (w).
- If q = +w, it means that the heat transfer is equal to the work done, which contradicts the first law of thermodynamics. Therefore, this option is incorrect.
(b) For an isochoric process, ΔU = -q:
- Isochoric means that the volume remains constant during the process.
- According to the first law of thermodynamics, the change in internal energy (ΔU) is equal to the heat transfer (q) minus the work done (w).
- If ΔU = -q, it means that the change in internal energy is equal to the negative of the heat transfer, which is correct for an isochoric process. Therefore, this option is correct.
(c) For an adiabatic process, ΔU = -w:
- Adiabatic means that there is no heat transfer during the process.
- According to the first law of thermodynamics, the change in internal energy (ΔU) is equal to the heat transfer (q) minus the work done (w).
- If ΔU = -w, it means that the change in internal energy is equal to the negative of the work done, which is correct for an adiabatic process. Therefore, this option is correct.
(d) For an isothermal irreversible change, q = -w:
- This option contradicts the first law of thermodynamics, which states that the change in internal energy (ΔU) is equal to the heat transfer (q) minus the work done (w). Therefore, this option is incorrect.
In conclusion, the correct options based on the first law of thermodynamics are: (b) For an isochoric process, ΔU = -q (c) For an adiabatic process, ΔU = -w
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