# Ideal gas law constant R conversion

1. May 6, 2004

### sitinduk

Hi, not sure if this is the right forum to ask this in, but I was trying to convert the ideal gas law constant R (from PV = nRT) from:

8.31 (Pa * cu. meters) / (mol * Kelvin) to the equivalent:

10.73 (psia * cu. ft) / (lb. * mol * Rankine)

Here's the conversion factors I've been using:
1 Pa = 1.4505E-7 psia (absolute pressure)
1 cu. meter = 35.315 cu. ft
1 Rankine = 1.8 Kelvin

What I don't understand is where does the extra pounds in the denominator of the 10.73 value come from? This is probably what's throwing off my calculations.

-Thanks

2. May 6, 2004

### Staff: Mentor

gm-Mole vs. lb-Mole

In the first equation "mole" means "gram-Mole"; in the second the unit is "lb-Mole". You need to convert between gm-Moles and lb-Moles.

3. May 6, 2004

### sitinduk

Ahh, using 1 gram = 0.0022 lb I finally got it. Thanks alot, this has really been bugging me

4. May 7, 2004

### MiGUi

I always use this
$$R = 0.082 \frac{atm \cdot l}{mol \cdot K} = 2 \frac{cal}{mol \cdot K} = 8.314 \frac{J}{mol \cdot K}$$

5. Jul 29, 2004

### evert

Take a look at:
http://www.adacs.com/menu/PDAcalc_units.php [Broken] This program runs on a palm, PocketPC,windows and will do all the conversions AUTOMATICALLY for you. Download the user manual which has an example of the PV = nRT formula that shows how it automatically convert between the different units.

Last edited by a moderator: May 1, 2017