(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Consider fuel cell using methane as fuel. Reaction is

CH^4 + 2O_2 -> 2H2O+CO_2

Assume room temperature and atmospheric temperature

Determine values of delta H (Helmholtz) and delta G (Gibbs) for this reaction for one mole of methane.

Question instructed the use of the web to find thermodynamic tables with values of H and G for the chemicals in the reaction

2. Relevant equations

I haven't encountered this sort of question where substitution of "real" values is necessary. Hence I've used this site as a reference:

http://members.aol.com/profchm/gibbs.html [Broken]

I think I found H alright (-802.3kJ), but to find G I need entropy (delta S)

3. The attempt at a solution

dG = dH - T.dS

dS = Sum of products (RHS) - Sum of reactants (LHS)

= [2(188.7)+213.7]-[186.3 + 2(205)]

= -5.2 (but isn't an entropy of less than zero impossible?)

The problem lies in the uncertainty of me obtaining an negative delta S

Thanks in advance for any hints/tips

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Thermo - Gibbs Free Energy & Entropy

**Physics Forums | Science Articles, Homework Help, Discussion**