Answer to Question #114281 in General Chemistry for Cesca

Question

Calculate the enthalpy of formation of ethanol (C2H5OH) given the following enthalpies of combustion.
ΔcH C(s) = -393, H2(g) = -286, C2H5OH(l) = -1371 kJ/mol

Answer 1

$4C+6H_2+O_2\to 2C_2H_5OH$ $\Delta fH=?$

$C+O_2\to CO_2$ $\Delta cH(C)=-393kJ/mol$

$2H_2+O_2\to2H_2O$ $\Delta cH (H_2)=-286 kJ/mol$

$C_2H_5OH+3O_2\to 2CO_2+3H_2O$ $\Delta cH(C_2H_5OH)=-1371kJ/mol$

$\Delta fH=4\Delta cH(C)+6\Delta cH(H_2)-2\Delta cH(C_2H_5OH)$

$\Delta fH=$ 4*(-393kJ/mol)+6*(-286kJ/mol)-2(-1371kJ/mol)=-546kJ/mol

Answer:-546kJ/mol