Question
For a reaction : $$X \to Y + Z$$
Absolute entropies are $$X = 120\,J\,{K^{ - 1}}\,mo{l^{ - 1}},$$ $$Y = 213.8\,J\,{K^{ - 1}}\,mo{l^{ - 1}}$$ and $$Z = 197.9\,J\,{K^{ - 1}}\,mo{l^{ - 1}}.$$
What will be the entropy change at $$298\,K$$ and $$1\,atm?$$
A.
$$291.7\,J\,{K^{ - 1}}$$
B.
$$255\,J\,{K^{ - 1}}$$
C.
$$213.8\,J\,{K^{ - 1}}$$
D.
$$257.3\,J\,{K^{ - 1}}$$
Answer :
$$291.7\,J\,{K^{ - 1}}$$
Solution :
$$\eqalign{
& \Delta {S^ \circ } = \sum {S_P^ \circ } - \sum {S_R^ \circ } \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\, = \left( {213.8 + 197.9} \right) - 120 \cr
& \,\,\,\,\,\,\,\,\,\,\,\,\, = 291.7\,J\,{K^{ - 1}} \cr} $$