Instant heat packs and cold packs use compounds that have a negative or positive enthalpy of solution, $\Delta H_{sol}$, to produce a temperature change. The packs consist of a pouch of water and a dry chemical, $CaCl_2$, for heat packs, or $NH_4NO_3$ for cold packs. The pack is activated by breaking the seal of the water pouch, which dissolves the dry chemical and forms a solution that either increases or decreases in temperature.
For the reaction
$NH_4NO_3(s) + H_2O(l) \rightarrow NH_4NO_3(aq)$
predict the sign of $\Delta H_{sol}$ for the solution.
$\Delta H_{sol} < 0$
$\Delta H_{sol} > 0$
$\Delta H_{sol} = 0$
Predict the sign of $\Delta S_{sol}$ for the solution.
$\Delta S_{sol} > 0$
$\Delta S_{sol} < 0$
$\Delta S_{sol} = 0$
For the reaction
$CaCl_2(s) + H_2O(l) \rightarrow CaCl_2(aq)$
predict the sign of $\Delta H_{sol}$ for the solution.
Predict the sign of $\Delta S_{sol}$ for the solution.
$\Delta H_{sol} < 0$
$\Delta S_{sol} > 0$
$\Delta H_{sol} = 0$
$\Delta S_{sol} = 0$
$\Delta H_{sol} > 0$
$\Delta S_{sol} < 0$
