Question

Using the information given in the reaction equations below, calculate the heat of formation for $1$ mole of carbon monoxide $CO$.
$2C\left(s\right)+2O_2\to 2C{O}_2$ $\Delta H_{rxn}=-787kJ$
$2CO+O_2\to 2C{O}_2$ $\Delta H_{rxn}=-566kJ$

• A. $-221kJ/mol$
• B. $-110kJ/mol$
• C. $110kJ/mol$
• D. $221kJ/mol$

Answer 1

Answer: (B)

$-110kJ/mol$

$2C+2O_2\to 2C{O}_2;$ ${\Delta }_1{H}_{rxn}=-787kJ$
$CO+O_2\to 2C{O}_2;$ ${\Delta }_2{H}_{rxn}=-566kJ$
Now, on substracting Equation-1 by 2:
$2C+O_2\to 2CO$
Hence, enthalpy of formation of 2 moles of CO$={\Delta }_1{H}_{rxn}-{\Delta }_2{H}_{rxn}=-787-(-566)=-221kJ$
$\frac{\Delta H_{rxn}}{2}=\frac{-221}{2}=-110.5kJ$= Enthalpy of formation of 1 mole of CO