Register to reply

Cp/Cv Value for H2O and H2

by ZA
Tags: cp or cv
Share this thread:
ZA
#1
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.
Phys.Org News Partner Science news on Phys.org
World's largest solar boat on Greek prehistoric mission
Google searches hold key to future market crashes
Mineral magic? Common mineral capable of making and breaking bonds
abercrombiems02
#2
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
Q_Goest
#3
Jul15-05, 10:17 AM
Sci Advisor
HW Helper
PF Gold
Q_Goest's Avatar
P: 2,903
I have a computer database that's giving me 1.257

Gokul43201
#4
Jul15-05, 10:35 AM
Emeritus
Sci Advisor
PF Gold
Gokul43201's Avatar
P: 11,155
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.


Register to reply