# Vapor pressure vs liquid pressure in enthalpic combustion reaction

1. Oct 10, 2010

### enantiomer

1. The problem statement, all variables and given/known data
Hi guys,
I'm a little lost on what should probably be a simple question
Using the following combustion reaction
(C7O2H6)s + 7.5 (O2)g --> 7 (CO2)g + 3 (H2O)l
the equation indicates that water produed by the reaction is liquid water not water vapor. Is this correct? Explain. The equilibrium vapor pressure of water is 22.38 torr at 24 C and 25.21 at 26 C.

2. Relevant equations
I think they're asking us to use ΔfH(l)[/SUP€]*Pp(l) + ΔfHg*Pp (g)
where Pp is the partial pressure of H2O as either a gas or a liquid and H is the enthalpy of formation of the either the liquid or the solid.
However now I'm stuck because I don't know how to get the partial pressures for the equation,
If I'm right with this equation can someone let me know what I'm missing?
If I'm wrong can someone tell me where I messed up?

Side note: I went to the TA and he mentioned that weighted averages should help with the reaction, but I'm still confused?