JEE Main · 2022 · 28 Jun 2022 · Shift 1 · Chemical Thermodynamics

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4.0 L of an ideal gas is allowed to expand isothermally into vacuum until the total volume is 20 L. The amount of heat absorbed in this expansion is ______ L atm.

Answer: 0

Solution

This is a free expansion (expansion into vacuum), where the external pressure

P_{ext} = 0

.

For free expansion:

Work done: $w = - P_{ext} Δ V = 0$
Since the process is isothermal for an ideal gas: $Δ U = 0$
From the first law: $q = Δ U - w = 0 - 0 = 0$

Therefore, no heat is absorbed or released during free expansion. The answer is 0 L atm.

JEE Main · 2022 · 28 Jun 2022 · Shift 1 · Integer answer

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