# Value of ideal gas constant R =?

Hi!

What is the value of the ideal gas constant R?
i see exercises are solved with either R=8,3 or R=0,0821
What is the difference between the two?
How do we know which to use when solving exercises?

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What is the difference between the different values for R?

The value of the ideal gas constant changes based on what units you are using.

R = 8.314 J/mol·K

This is when we are working with mol and Kelvin.

It all depends on the units you are using for temperature, pressure and volume.

R = 0.0821 L·atm/mol·K

1 atm = 101.33 kPa
1 J = 1 L·kPa= 101.33 L·atm, so the difference between the two:

\frac{8.314 J/mol·K}{101.33 L·atm} =R = 0.0821 L·atm/mol·K

So how do we know when to use which?

More often you will see R=8.3 because this is the value used with Volume = L, Pressure = kPa, and Temperature = Kelvin. (normal SI units). So we are using Joules here which are interchangeable with L·kPa, the units for the pressure you are often solving for.

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