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Cp/Cv Value for H2O and H2

by ZA
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Jul14-05, 11:13 PM
P: 13
I need to find out the Cp/Cv value for Water Vapor and Hydrogen gas at 2755 K and a molar ratio of: H2O/H2:48.6112/62.5 I would at least like the Cv and Cp values for water vapor at 2755 K. A correct answer will be greatly appreciated.
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Jul15-05, 12:13 AM
P: 114
from the equation in my thermodynamic textbook this is my equation

Cp(T) steam = 32.24 + 0.1923e-2*T + 1.055e-5*T^2 - 3.595e-9*T^3

However, there are a few things i need to mention here

First the units are kJ/kmol-K so you need to divide by 18 to get kJ/kg-K

Also, this equation is over the range of 273K - 1800K with a maximum error of 0.53%, so its pretty small, If i use the same equation at 2755 K I get

Cp(2755) Steam = 42.4393 kJ/kmol-K or

Cp(2755) Steam = 2.35 kJ/kg-K

As for the Cv values, my text does not have an equation
Jul15-05, 10:17 AM
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I have a computer database that's giving me 1.257

Jul15-05, 10:35 AM
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Cp/Cv Value for H2O and H2

Quote Quote by abercrombiems02

Cp(2755) Steam = 42.4393 kJ/kmol-K or ...

As for the Cv values, my text does not have an equation
You could use Cp - Cv = R = 8.314 kJ/K-kmol, as a pretty good approximation.

So, Cv = 42.439 - 8.314 = 34.125 kJ/K-kmol

Hence, Cp/Cv = 1.244, which is not too far from the number quoted by Q_Goest.

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