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Topic: Thermochemistry  (Read 12251 times)

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Offline ebaugh

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Thermochemistry
« on: November 13, 2007, 09:16:46 PM »
A sample of 2.00 mol CH3OH(g) is condensed isothermally and reversibly to liquid at 64°C. The standard enthalpy of vaporization of methanol at 64°C is 35.3 kJ mol−1. Find w, q, ∆U, and ∆H for this process.

I know the basic relationships for this type of process. I just dont know where to start with the dH(vaporization).

Offline Disturbia

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Re: Thermochemistry
« Reply #1 on: November 14, 2007, 12:50:30 AM »
A sample of 2.00 mol CH3OH(g) is condensed isothermally and reversibly to liquid at 64°C. The standard enthalpy of vaporization of methanol at 64°C is 35.3 kJ mol−1. Find w, q, ∆U, and ∆H for this process.

I know the basic relationships for this type of process. I just dont know where to start with the dH(vaporization).

you can find w = -nRT ln(Vf/Vi) for an ideal gas
H = U + pv = U + RT delta(n)
you will find U
then u = q + w


Offline enahs

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Re: Thermochemistry
« Reply #2 on: November 14, 2007, 09:15:44 PM »
Take some time to study and focus on what your keywords means, such as isothermal and reversible in this case.

These key words tell you a lot. And typically in most problems assigned by professors, those key words tell you what one (or more!) of the 4 common values you are asked to find (which, is your case) without doing a single calculations. This then simplifies all your other calculations and you find things start getting much simpler to calculate, even trivial!


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