# Why must only SI units be used when making calculation using the ideal gas equation?

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• You can use any set of consistent units

• Anonymous
5 months ago

Why must?

the short answer is you don't.

• you can use any units you want as long as you use the value of the gas constant that applies to those units.

reference has a list of 20 or so values for R, including ones with temp in rankine, and volume in cubic feet.

https://www.cpp.edu/~lllee/gasconstant.pdf

• pisgahchemist
Lv 7
6 months agoReport

I agree with billrussell. You can use any number of units for P, V and T, as long as you've got R defined in those units. The atmosphere (atm) isn't an SI unit and we use it all the time. The SI unit for pressure is the pascal.

• So people from around the world can read and understand what you calculated and noted

• Primarily because that's the way it is taught. The equation still holds, but the units are very different. and the arithmetic is a bit trickier, even though the same equation still holds.

Imperial (or English) units can be used as in:

https://www.me.psu.edu/cimbala/Learning/General/Ga...

• The constant R is 22.4 liters divided 273˚K

R = 22.4 ÷ 273

This is approximately 0.08205. 22.4 is the number of liters of one mole of a gas at standard temperature and pressure.

P * V = n * R * T

P is in atmospheres. V is in liters. n is the number of moles. T is the temperature in ˚K. If we used different units, the value of the ideal gas constant would have to be different.

• probably the reason is the formulas are writen that way ..

Kelvin temps re used because they are all positive

land the pressures hve to apply to the pressure of the equation so the result is accurate to the data given and the result wanted ..