$(i)$ $NH_3$ $_{(g)} + aq$ $\rightarrow$ $NH_3$ $_{(aq)}$, $\Delta H$ $= -8.4 \,Kcal.$
$(ii)$ $HCl_{(g)} + aq$ $\rightarrow$ $HCl{(aq)}$, $\Delta H =$ ${-1}7.3\, Kcal.$
$(iii)$ $NH_3$ $_{(aq)} + HCl_{(aq)}$ $\rightarrow$ $NH_4Cl $ $_{(aq)}$, $\Delta H = -12.5\, Kcal$.
$(iv)$ $NH_4Cl$ $_{(s)} + aq$ $\rightarrow$ $NH_4Cl$ $_{(aq)}$, $\Delta H = +3.9 \,Kcal.$
$KC{l_{\left( s \right)}} + 20{H_2}O \to KCl\,\left( {20\,{H_2}O} \right);\Delta H = + 15.90\,kJ$
$KC{l_{\left( s \right)}} + 200{H_2}O \to KCl\,\left( {200\,{H_2}O} \right);\Delta H = + 18.58\,kJ$