$2Fe + 1/2{O_2} \to F{e_2}{O_3} + y\,kcal$ હોય, તો $Fe$ અને ઓક્સિજન માંથી$F{e_2}{O_3}$ ના સર્જનની ઉષ્મા ... થશે.
$ii)$ $2 FeO +\frac{1}{2} O _2 \longrightarrow Fe _2 O _3 \quad \Delta H _{ ii }=-y$
$iii)$ $2 Fe +\frac{3}{2} O _2 \longrightarrow Fe _2 O _3 \quad \Delta H =(?)$
$(iii)$ $=2( i )+2($ ii $)$
$\therefore \Delta H =\Delta H _i+\Delta H _{ ii }=-2 x +(- y )=-(2 x + y )$
$N{H_{3(g)}}\, + \,\,\frac{3}{2}\,Cu{O_{(s)}}\, \to \,\,\frac{1}{2}\,{N_{2(g)}}\, + \,\,\frac{3}{2}{H_2}{O_{(\ell )}}\, + \,\,\frac{3}{2}\,C{u_{(s)}}.$ ......$J$
$KC{l_{\left( s \right)}} + 20{H_2}O \to KCl\,\left( {20\,{H_2}O} \right);\Delta H = + 15.90\,kJ$
$KC{l_{\left( s \right)}} + 200{H_2}O \to KCl\,\left( {200\,{H_2}O} \right);\Delta H = + 18.58\,kJ$
$A.$ $I _2( g ) \rightarrow 2 I ( g )$
$B.$ $HCl ( g ) \rightarrow H ( g )+ Cl ( g )$
$C.$ $H _2 O ( l ) \rightarrow H _2 O ( g )$
$D.$ $C ( s )+ O _2( g ) \rightarrow CO _2( g )$
$E.$ પાણીમાં એમોનિયમ કલોરાઈડનું વિલયન (ઓગળવું)