The Standard Entropy of Reaction, _ Sorxn
For many chemical reactions:
_ So = Soproducts - Soreactants > 0
Standard entropy of reaction, _ Sorxn:
But for reactions in which the total # of moles of products decrease,
particularly gases which have very high entropy, we predict that the
entropy of the products is less than that of the reactants. Therefore,
the entropy will decrease during the reaction:
N2 (g) + 3 H2 (g) 2 NH3 (g) _ So = Soproducts - Soreactants< 0
_ Sorxn = (2 mol NH3 x So of NH3) - [(1 mol x 191.5 J/mol K) +
(3 mol x 130.6 J/mol K)]
_ Sorxn = -197 J/K
.
.
As predicted, _ So < 0
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