### Using ideal gas constants

Posted: **Mon Jan 11, 2016 9:38 pm**

by **Daniel Zhang 1E**

How do we know when or what gas constants to use when calculating for the change in internal energy of a gas with constant pressure? For example, 8.9 from the textbook uses 8.314 and 0.08206, but how did they know to use these constants?

### Re: Using ideal gas constants

Posted: **Mon Jan 11, 2016 9:49 pm**

by **Ronald Yang 2F**

The easiest way is to look at the units for each constant. For 0.08206, that is in the unit (atm*L)/(mol*K). For 8.314, that is in the unit J/(mol*K). They are essentially the same thing other than the units. You can go from 0.08206 to 8.314 by using the conversion 101.325 J/(atm*L). Based on the information given in terms of the units of numbers a problem gives, you would use either one for convenience.