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Can someone help me with this? watch

1. Assuming that you have the ∆G*f for the components of the combustion of Ethanol and you need to figure out the ∆G* of the entire reaction. How do I do it?

O2 (g) = 0 kJ/mol
C2H5OH (l) = -174.8 kJ/mol
H2O (l) = -237.2 kJ/mol
CO2 (g) = -394.4 kJ/mol

P.S. If I can have a better way to format equations, that would be appriciated.
2. You need to use hess's law: the energy for a process is the same regardless of the route taken.

Taking the balance equation:

C2H5OH + (7/2)O2 ----> 2CO2 + 3H2O

One mole of ethanol produces 2 moles of CO2 (2 x -394.4 kJ/mol) and 3 moles of H2O (3 x -237.2 kJ/mol) - so the energy at the end is -1500.4 kJ/mol. At the start ∆G of formation for elements (such as oxygen) is zero so that leaves -174.8 kJ/mol.

∆G = ∆G(products) - ∆G(reactants)

so ∆G = -1500.4 - (-174.8) = -1325.6 kJ/mol

p.s. I see why you asked now
3. I'd assume it's the same as enthalpy change; write the equation for the combustion of ethanol, write the elements beneath them, and draw 2 arrows up from the elements to products and reactants. Put in the values for these, then add some things together (Remember it's negative the value on the arrow going to ethanol)

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Updated: November 12, 2008
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