Problem $-84-$ Experiment $4$

The cooling power of the dissolution reaction below is being evaluated.

$N{H}_{4}N{O}_3(s)N{H}_4^{+}(aq)+N{O}_3^{-}(aq)$

a$.$ A calorimeter is constructed and found to have a calorimeter constant of $84\mathrm{.}5J{K}^{-1}.$ A $100\mathrm{.}0g$ quantity of water is placed inside. The device and its contents come to room temperature, which is $25\mathrm{.}00C.$ Then $3\mathrm{.}20g$ of $N{H}_{4}N{O}_3(s)$ is added to the water. It dissolves, causing the temperature inside the calorimeter to fall to $22\mathrm{.}93.$ Compute $H_r($in kJ mol ${?}^{-1})$ for the dissolution. List the approximations and assumptions that must be made.

b$.$ Compute $H_r$ using the standard molar enthalpies of formation tabulated in Appendix D$.$

c$.$ List and discuss the reasons for the slight difference between the answers to parts $($a$)$ and $($b$).$