How to Convert Ideal Gas Constants from Mass-Based Units to Molar-Based Units?

[2h2o]

[SOLVED] Ideal gas unit conversions

Homework Statement

The ideal gas constants used in this text are typically mass-based: kJ / (kg*K). It is more useful to have them in units of kJ / (kmol*K). How to convert them using data from this text?

Homework Equations

The Attempt at a Solution

I'd think that this is a problem in which I'd consult the periodic table to obtain the molecular mass of a given compound, but the P. table is not included. I have steam tables, gas-constant/critical point properties tables, etc. Seems like such a simple question, yet I'm not seeing the path. Can anyone point me in the right direction?

 

[SteamKing]

You have a computer. Surely you can find a periodic table somewhere on the internet.

 

[2h2o]

Yes, obviously. I also have numerous chemistry books. But the problem specifically states to use data contained within the text--there is no periodic table within. Hence, my confusion.

Converting grams to moles is trivial with a PT. Without the PT; I don't understand...

 

[2h2o]

Nevermind, I found a table in the text that lists molecular masses of some selected compounds. The problem is reduced to triviality, afterall.

Wouldn't it be much simpler to just include a PT on the frontsheet or at least appendix, like every other science book I've encountered? What kind of Thermodynamics book wouldn't include one? Silly!

Cheers

 

[DeeNos]

To convert ideal gas constants from mass-based units (kJ/(kg*K)) to molar-based units (kJ/(kmol*K)), we can use the molar mass of the gas. The molar mass is the mass of one mole of a substance and can be found on the periodic table. To convert from mass-based units to molar-based units, we can use the following equation:

R_molar = R_mass / M

Where:
R_molar is the gas constant in molar-based units (kJ/(kmol*K))
R_mass is the gas constant in mass-based units (kJ/(kg*K))
M is the molar mass of the gas in kg/kmol.

For example, if we have a gas with a mass-based gas constant of 0.082 kJ/(kg*K), and a molar mass of 18 kg/kmol (which is the molar mass of water vapor), we can convert the gas constant to molar-based units as follows:

R_molar = 0.082 kJ/(kg*K) / 18 kg/kmol = 0.0046 kJ/(kmol*K)

Therefore, the gas constant in molar-based units is 0.0046 kJ/(kmol*K). This conversion can be applied to any gas using its respective molar mass.