Predict the sign of `DeltaS` in the following processes. Give reasons for your answer.
(a) `N_(2(g))+3H_(2(g))rarr2NH_(3(g))`
(b) `CO_(2(g))rarrCO_(2(s))`

Explanation

(a) `N_(2(g))+3H_(2(g))rarr 2NH_(3(g))`
In the reaction, 4 moles of gaseous reactants form 2 moles of gaseous products `(Delta n lt 0).` Therefore disorder decreases and hence entropy decreases. `DeltaS lt 0.`
(b) `CO_(2(g))rarrCO_(2(s))`
In this system from higher disorder ingaseous state changes to less disorder in the sollid state, hence entropy decreases, `DeltaSlt0`.