The Student Room Group
Uni students - Complete our survey >>
Uni students - Complete our survey >>
Uni students - Complete our survey >>

Hess' Law

Could someone please explain how I would answer this question:

Calculate the enthalpy of formation of ethanol (C2H5OH) given the following enthalpies of combustion.

C(s) -393
H2(g) -286
C2H5OH(l) -1371


I've got the answer as -273 but I'm not too sure
(edited 9 years ago)
Original post by lucindaaa
Could someone please explain how I would answer this question:

Calculate the enthalpy of formation of ethanol (C2H5OH) given the following enthalpies of combustion.

C(s) -393
H2(g) -286
C2H5OH(l) -1371


I've got the answer as -273 but I'm not too sure


:smile:
Reverse the enthalpy of combustion equation for ethanol, change this equation to make it so that CO2 changes to C and H2O changes to H2. Add together all the enthalpies needed to do this.
e.g.
C2H5OH+3O2⟶2CO2+3H2OC_2H_5OH+3O2 \longrightarrow 2CO_2+3H_2O ΔH∘=−1371kJmol−1\Delta H^{\circ}=-1371 kJ mol^{-1}

becomes

2CO2+3H2O⟶C2H5OH+3O22CO_2+3H_2O \longrightarrow C_2H_5OH+3O2 ΔH∘=+1371kJmol−1\Delta H^{\circ}=+1371 kJ mol^{-1}

Then

Make it so

2C+3H2+1/2O2⟶C2H5OH 2C+3H_2+1/2O_2 \longrightarrow C_2H_5OH

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you