[neon flash!]

1) The physical properties of the structural isomers of C8 alkanes are significantly different, as are their free energies of formation:

C8 alkane   ∆G˚f / kJ mol-1
Octane   16.3
2-Methylheptane   11.7
3,3-Dimethylhexane   12.6

Each compound burns according to the chemical equation:

2 C8H18(l) + 25 O2(g) → 16 CO2(g) + 18 H2O(g)

Predict whether ∆G˚rxn of the combustion reactions of these isomers will be the same of different. Explain your answer.

i think the delta g would be the same. its the same compound. onthe other hand wont it have to do with bond breaking etc. if the structure is different perhaps in certain positions the bonds are require less energy to break.

Q2)Calculate the value of ∆G for the cell reaction in the lead-acid batteries used to start car and truck engines if each cell in the battery produces 2.04 V. The cell reaction is:

Pb(s) + PbO2(s) + 2 H2SO4(aq) → 2 PbSO4(s) + 2 H2O(l)
i need to identify the oxidised and reduced species.
the Pb is being oxidised from Pb(s) to Pb2+
i'm not sure what is being reduced? the H?
then i use delta G = nFE
where n will be the no of electrons and E will be 2.04?

[UG]

Predict whether ∆G˚rxn of the combustion reactions of these isomers will be the same of different. Explain your answer.

i think the delta g would be the same. its the same compound. onthe other hand wont it have to do with bond breaking etc. if the structure is different perhaps in certain positions the bonds are require less energy to break.

How would you calculate the ∆G˚rxn of 2 C₈H₁₈(l) + 25 O₂(g) → 16 CO₂(g) + 18 H₂O(g) if you were given a table of standard free energies of formation?

[neon flash!]

i think it would be like sum of energies of formations of products - sum of energies of formations of reactants?

[UG]

Ok, so if the standard free energy of formation of CO₂ is -394.4 kJ/mol and that of H₂O(g) was -228.6 kJ/mol, what is the ∆G˚rxn for the reaction:

2 C₈H₁₈(l) + 25 O₂(g) → 16 CO₂(g) + 18 H₂O(g)

for the three compounds octane, 2-methylheptane and 3,3-dimethylhexane   

[Dan]

Pb(s) + PbO2(s) + 2 H2SO4(aq) → 2 PbSO4(s) + 2 H2O(l)
i need to identify the oxidised and reduced species.
i'm not sure what is being reduced? the H?

No, not H. You know the lead in the products is Pb²⁺, so what are the oxidation numbers of lead in the starting materials?