Question

What will be the heat formation of methane; if the heat of combustion of carbon is '$-x$' $kJ$, heat of formation of water is '$-y$' $kJ$ and heat of combustion of methane is '$-z$' $kJ$?

• A. $(-x-y-z)kJ$
• B. $(-z-x+2y)kJ$
• C. $(-x-2y-z)kJ$
• D. $(-x-2y+z)kJ$

Answer 1

Answer: (D)

$(-x-2y+z)kJ$

Formation of methane $\Rightarrow C+2H_{2}O\to {CH}_4+O_2$

$\therefore$ Heat of formation of methane $={\Delta }_c\left(C\right)-{\Delta }_c\left({CH}_4\right)-2\times {\Delta }_f\left(H_{2}O\right)$

$=-x-(-z)-2y$

$=(-x+z-2y)kJ$

$=(-x-2y+z)kJ$