The molar heat of solution of in liquid at this concentration is — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

Molar mass of $\text{NH}_4\text{Br} = 98\text{ g/mol}$. Moles dissolved = $0.98 / 98 = 0.01\text{ mol}$. The dissolution caused $0.25\text{ g}$ of $\text{NH}_3$ to vaporize, meaning heat was strictly released (exothermic). Heat released = $0.25\text{ g} \times 320.0\text{ cal/g} = 80\text{ cal}$. Thus, $\Delta H = -80\text{ cal} / 0.01\text{ mol} = -8000\text{ cal/mol} = -8.0\text{ kcal/mol}$.