Vapor pressure vs liquid pressure in enthelpic combustion reaction

[enantiomer]

Homework Statement

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.

Homework Equations

I think they're asking us to use Δ_fH<sup>(l)[/SUP€]*P_p(l) + Δ_fH_g*P_p (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?
Thanks in advance</sup>

 

[nate808]

Hello,

You are on the right track with using the enthalpy of formation and partial pressures to determine the state of water in this reaction. However, there are a few things you are missing.

Firstly, the equilibrium vapor pressure of water is important to consider in this reaction. Since the reaction is taking place at a temperature between 24 C and 26 C, we can assume that the partial pressure of water vapor will be between 22.38 torr and 25.21 torr. This means that the partial pressure of water vapor in the reaction will be less than the equilibrium vapor pressure, and therefore, the water produced will be in liquid form.

Secondly, you need to consider the stoichiometry of the reaction. The given equation shows that for every 7.5 moles of oxygen gas, 3 moles of water are produced. This means that the partial pressure of water vapor will be 3/7.5 times the partial pressure of oxygen gas.

Finally, to determine the partial pressure of water vapor, you can use the ideal gas law: PV = nRT. Since you know the temperature and the partial pressure of oxygen gas, you can solve for the partial pressure of water vapor.

I hope this helps. Let me know if you have any further questions. Good luck with your work!