Question

A scientist measures the standard enthalpy change for the following reaction to be -104.6 kJ :

CO(g) + Cl2(g)COCl2(g)

Based on this value and the standard enthalpies of formation for the other substances, the standard enthalpy of formation of CO(g) is __kJ/mol.

Answer 1

The standard enthalpy change for the reaction is the difference between standard enthalpies of formation for products multiplied by their stoichiometric coefficients and standard enthalpies of formation for reactants multiplied by their stoichiometric coefficients

For the reaction above ∆_rH=∆_fH(COCl₂)-∆_fH(CO)-∆_fH(Cl₂)

Thus, ∆_fH(CO)=-∆_rH+∆fH(COCl2)+∆fH(Cl2)

∆fH(Cl2)=0 kJ/mol

∆fH(COCl2)=-218.0 kJ/mol

∆fH(CO)=-(-104.6)+(-218.0)+0=-113.4kJ/mol