If ΔU and ΔW denote the increase in internal energy and work done by the system respectively in a thermodynamic process, which of the following is true?
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Question

If ΔU and ΔW denote the increase in internal energy and work done by the system respectively in a thermodynamic process, which of the following is true?

G1 Physics · Accepted Answer

Step 1: Apply the first law with the convention that ΔW denotes work done BY the gas: ΔQ = ΔU + ΔW. Step 2: In an adiabatic process, no heat crosses the system boundary, so ΔQ = 0. Step 3: Hence 0 = ΔU + ΔW, giving ΔU = −ΔW. Step 4: For an ideal gas in an isothermal process, ΔU = 0, but ΔW need not be zero; that eliminates the isothermal alternatives. Final answer: (A).