Question

$20$ grams of Neon(At. Wt $=20$) initially at a pressure of $506.625$ kPa and temperature of $475$K expanded adiabatically to a pressure of $50.6625$ kPa. Which of the following is/are correct, when the expansion is a free expansion?
(i) $W=0$
(ii) $q=0$
(iii) $dE=0$
(iv) Temperature of the gas remains unchanged during the expansion.

• A. i, ii and iii
• B. ii, iii and iv
• C. i, ii, iii and iv
• D. iv only

Answer 1

Answer: (C)

i, ii, iii and iv

Solution:- (C) i, ii, iii and iv

In a free expansion,

$W=0$

Since the expansion is adiabatic.

$\therefore q=0$

Now from first law of thermodynamics,

$\Delta U=q+W=0$

Hence the temperature of the gas remains unchanged during expansion.

Hence all are correct.