NEET 2020 · ChemistryPrevious Year Question

The correct option for free expansion of an ideal gas under adiabatic condition is:

Answer: (C) $q = 0$ , $Δ T = 0$ and $w = 0$ . \textbf{Answer:} (C) $q = 0$ , $Δ T = 0$ and $w = 0$ \textbf{Solution:} In free expansion the gas expands into vacuum, so the external pressure is zero and $w = - p_{e x t} Δ V = 0$ .

A. $q < 0$ , $Δ T = 0$ and $w = 0$
B. $q > 0$ , $Δ T > 0$ and $w > 0$
C. $q = 0$ , $Δ T = 0$ and $w = 0$ ✓
D. $q = 0$ , $Δ T < 0$ and $w > 0$

Correct Answer

Solution & Explanation

\textbf{Answer:} (C) $q = 0$ , $Δ T = 0$ and $w = 0$ \textbf{Solution:} In free expansion the gas expands into vacuum, so the external pressure is zero and $w = - p_{e x t} Δ V = 0$ . Adiabatic means $q = 0$ . By the first law $Δ U = q + w = 0$ , and for an ideal gas $Δ U = n C_{v} Δ T$ , so $Δ T = 0$ .

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