A sample containing 2.000 mol of helium gas originally at 298.15 K and 1.000 bar is cooled to its norm boiling temperature of 4K, condensed to a liquid and then cooled further to 2 K, where it undergoes anoth phase transition to a second liquid form, called liquid helium II. Abeam of laser light suddenly vapourizes th liquid phase, and the helium is brought to a temperature of 298.15 Ķ and a pressure of 0.500 bar. The entropy change for the above process is:

Options

A. `11.5 JK ^(-1)`
B. `- 11. 5 JK ^(-1)`
C. `23 JK ^(-1)`
D. `- 23 JK ^(-1)`

Explanation

Entropy, a state function, does not depends on path . Hence, for `He (g) [ 2 mol, 298 . 1 5 K, 1. 00 ` bar]
Initial : `H e (g) [ 2 mol , 2 98 . 15 K, 0. 500 ` bar]
Final `: Delta S = n R ln ""(P _(1))/( P _(2)) = 2 R ln 2 = 11. 5 JK ^(-1) `