Entropy Quiz 8

1
Entropy Quiz 8 The monatomic gas, Ne, is a
mixture of the following naturally occurring
isotopes atomic weight weight natural
abundance 20Ne 19.99 amu 89.67 weight 21Ne
20.99 amu 0.28 weight 22Ne 21.99
amu 10.05 weight What is the entropy of
mixing, ?Smixing, in Joules/(mol K) that is
inherently present in naturally occurring
Ne? convert the weight percents to mole percent
(assume 100 grams total) ( 100.0 g ) ( 0.8967 )
/ 19.99 4.486 mols of 20Ne ( 100.0 g )
( 0.0028 ) / 20.99 0.01334 mols of 21Ne (
100.0 g ) ( 0.1005 ) / 21.99 0.4570 mols
of 22Ne n total (4.486 mols)
(0.01334 mols) (0.4570 mols) 4.956
moles calculate the mole fractions X 20Ne
4.486 moles / 4.956 mols 0.9051 X
21Ne 0.01334 moles / 4.956 mols 0.002692
X 22Ne 0.4570 moles / 4.956 mols 0.09220
2
calculate the entropy of mixing per mole
?Smixing, - R S Xi ln Xi - R X
20Ne ln ( X 20Ne ) X 21Ne ln ( X 21Ne )
X 22Ne ln ( X 22Ne ) - (8.314 J
/ (mol K) 0.9051 ln (0.9051)
0.002700 ln (0.002700) 0.09220 ln
(0.09220) 2.71 J / ( mol K )