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Consider the reaction for the dissolution of ammonium nitrate: `NH_(4)NO_(3)(s) rarr NH_(4)^(o+)(aq) +NO_(3)^(Theta) (aq)` `DeltaH =+29.8 KJ mol^(-1), DeltaS = 108.0 J K^(-1) mol^(-1)`. Calculate the change in entropy of the surroundings and predict whether the reaction is spontaneous or not at `25^(@)C`? |
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Answer» The reaction is endothermic, `DeltaH = 29.8 k J mol^(-1)` `:.` Entropy change in surroundings `Delta_(surr)S =- (Delta_(sys)H)/(T) =- (29.8 xx 10^(3))/(298) =- 100.0 J K^(-1) mol^(-1)` `Delta_(sys)S = 108.0 J K^(-1) mol^(-1)` `:. Delta_("total")S = Delta_(sys)S + Delta_(surr)S = 108.0 - 100.0` `= 8.0 J K^(-1) mol^(-1)` There is increase in total enegry so ammonium nitrate dissolves spontaneously. |
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