Chapter 9, Problem 9.8A

• APPLY 9.8 Instant hot packs and cold packs contain a solid salt in a capsule that is broken and dissolved in water to produce a temperature change. Which of the following salts would result in greatest decrease in temperature when dissolved in 100,0 mL of water in a cold pack? Use the following thermochemical data to answer the question.

$\text{LiF(s)}\to L{i}^{+}(aq)+{\text{F}}^{-}(aq)$ $\Delta H°$= +5.5kJ

$\text{LiCl(s)}\to {\text{Li}}^{+}(aq)+C{l}^{-}(aq)$ $\Delta H°$= -37.1 kJ

${\text{BaSO}}_{\text{4}}\text{(s)}\to {\text{Ba}}^{\text{2}+}(aq)+{\text{SO}}_{\text{4}}{}^{\text{2}-}(aq)$ $\Delta H°$= +26.3 kJ

${\text{CaCl}}_{\text{2}}\text{(s)}\to C{a}^{2+}(aq)+{\text{2Cl}}^{-}(aq)$ $\Delta H°$= -81.8 kJ

(a) 10.0 g of LiF
(b) 10.0 g of BaSO₄
(c) 10.0 g of LiCl
(d) 10.0 g of CaCl₂

• Instant cold packs are used to treat athletic injuries.