Question

The decomposition of mercuric oxide ($Hg)$) on heating, resulting in the formation of mercury and oxygen, is represented by the following chemical equation-
$2HgO+180kJ⟶2Hg+O_2$
Which one of the following represents the heat of formation of mercuric oxide?

• A. $5.66kJ{mole}^{-1}$
• B. $90kJ{mole}^{-1}$
• C. $180kJ{mole}^{-1}$
• D. $900kJ{mole}^{-1}$

Answer 1

The correct option is B $90kJ{mole}^{-1}$

Mercuric oxide gives mercury and oxygen on heating
$2HgO+180kJ⟶2Hg+O_2$
The following represents the heat of formation of mercuric oxide.
$Hg+\frac{1}{2}{O}_2⟶HgO+90kJ$
The heat of formation is the enthalpy change for the formation of $1$ mole of $HgO$.