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Topic: liquid pressure vs. vapor pressure  (Read 2298 times)

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Offline Enantiomer

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liquid pressure vs. vapor pressure
« on: October 10, 2010, 10:39:16 AM »
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.

I think they're asking us to use ΔH(l)*Pp(l) + ΔHg*Pp (g)
where Pp is the partial pressure of H20 as either a gas or a liquid and H is the enthalpy 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?

Offline Borek

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Re: liquid pressure vs. vapor pressure
« Reply #1 on: October 10, 2010, 03:53:59 PM »
In general below 100 deg C you can assume water is being produced as a liquid, above - as a gas. That's only approximation and in some cases it is not accurate enough, so a lot depends on the context of the question. If it is just a general chemistry, that should be OK.
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