Hi Borek. Thanks for replying.

So, I got them. Methane at -890.3 and Propane at -2219.1. Is it just a matter of solving for x in an equation like this:

-890.3x + -2219.1y = -776 kJ

And that will give me the moles of x, at which point I use the total moles I previously found to get the mole fraction?

y being (0.512-x),

so -890.3x + (-2219.1)(.512-x) = -776kJ

x = .27 mol / .512total moles = 53% CH

_{4}Is that correct?

//edit: Incorrect. Got it wrong.

'supposed to be 42.7%. Don't know where that came from