Discussion in 'Electronics Homework Help' started by Jayce, Jan 25, 2019.

1. ### Jayce

7
0
Mar 24, 2018

How to convert J/mol-K to BTU/mol-R? Example 8.314 J/mol-K to BTU/mol-R?

What I know is that 1 BTU = 1056 Joules and that Kelvin = 1.8 Rankine. So:
(8.314 J/mol-K)(1 BTU/1056 J)(1 K/ 1.8 R) = 4.3739 x 10^-3 BTU /mol-R. But the answer is supposed to be 1.986.

Any help would be appreciated, thank you.

2. ### Harald KappModeratorModerator

8,830
1,741
Nov 17, 2011
Don't feel sorry for asking, that's what this forum is for.
I would calculate in the same way as you did, arriving at the same answer.

Where does the proposed solution come from?

3. ### Jayce

7
0
Mar 24, 2018
Thank you for the response. It's from the Universal Gas Constant "R". R = 8.314 J/mol-K = 1.986 BTU/mol-R = 1545 ft-lb/mol-R
I'm not good at memorization so I plan to just memorized one then learn how to convert it to the other unit/s.

4. ### Ratch

1,025
302
Mar 10, 2013
Me thinks you have your units scrambled. I did the calculation for units of calories/(mole-kelvin) and I get 1.986. See below.

Ratch

5. ### Harald KappModeratorModerator

8,830
1,741
Nov 17, 2011
Sounds reasonable: cal, not BTU then

6. ### Jayce

7
0
Mar 24, 2018
No, the 1.986 should be in BTU/mol-R not cal/mol-K. (Although what you calculated is right if we're talking about cal/mol-K)
An image below shows the conversion for the universal gas constants. It is from my physics book. (2 different books have the same conversions, so I don't think it's a typo.) Sorry if the image is not good.

File size:
44.9 KB
Views:
4
7. ### Ratch

1,025
302
Mar 10, 2013
The book's figure of 1545 is for English units of lbf-ft, rankine,and lb-moles. However, the book does not tell you that. Get a different text book.

Ratch