\(\mathop {{C_6}{H_{10}}}\limits_{Cyclohexene} + {H_2} \to \mathop {{C_6}{H_{12}},}\limits_{Cyclohexane} \,\,\,\,\,\,\,\,\,\,\,\Delta {H_1} = ?.....(1)\)
Let us write the given facts
\({H_2} + \frac{1}{2}{O_2} \to {H_2}O;\)
\(\Delta {H_2} = - 241\,\,kJ/mol.....(2)\)
\({C_6}{H_{10}} + \frac{{17}}{2}{O_2} \to 6C{O_2} + 5{H_2}O,\)
\(\Delta {H_3} = - 3800\,kJ/mol.....(3)\)
\({C_6}{H_{12}} + 9{O_2} \to 6C{O_2} + 6{H_2}O,\)
\(\Delta {H_4} = - 3920\,kJ/mol.....(4)\)
The required reaction \((1)\) can be obtained by adding equations \((2)\) and \((3)\), and subtracting \((4)\) from the sum of \((2)\) and \((3)\).
\({C_6}{H_{10}} + {H_2} \to {C_6}{H_{12}}\)
\(\Delta {H_1} = (\Delta {H_2} + \Delta {H_3}) - \Delta {H_4}\)
\( = [ - 241 + ( - 3800)] - ( - 3920)\)
\( = ( - 241 - 3800) - ( - 3920)\)
\( = - 4041 + 3920 = - 121\,kJ/mol\)
(તટસ્થીકરણ એન્થાલ્પી $=57\, kJ \,mol ^{-1}$ અને પાણીની વિશિષ્ટ ઉષ્મા= $4.2 \,J\,K ^{-1} \,g ^{-1}$ )