# Question 19.3: Calculating ΔS° for a Reaction Calculate the change of entro...

**Calculating** \Delta S^{\circ} **for a Reaction**

Calculate the change of entropy, \Delta S^{\circ}, at 25^{\circ} \mathrm{C} for the reaction in which urea is formed from \mathrm{NH}_{3} and \mathrm{CO}_{2}.

2 \mathrm{NH}_{3}(g)+\mathrm{CO}_{2}(g) \longrightarrow \mathrm{NH}_{2} \mathrm{CONH}_{2}(a q)+\mathrm{H}_{2} \mathrm{O}(l)

The standard entropy of \mathrm{NH}_{2} \mathrm{CONH}_{2}(a q) is 174 \mathrm{~J} /(\mathrm{mol} \cdot \mathrm{K}). See Table 19.1 for other values.

**PROBLEM STRATEGY**

The calculation is similar to that used to obtain \Delta H^{\circ} from \Delta H_{f}^{\circ} values.

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