# Question #da257

Mar 5, 2014

The units of Ideal gas law constant is derived from equation
PV = nRT.

Where the pressure - P, is in atmospheres (atm) the volume - V, is in liters (L) the moles -n, are in moles (m) and Temperature -T is in Kelvin (K) as in all gas law calculations.

When we do the algebraic reconfiguration we end up with Pressure and Volume being decided by moles and Temperature, giving us a combined unit of atm x L / mol x K. the constant value then becomes 0.0821 atm(L)/mol(K).

If you choose not to have your students work in standard pressure unit factor, you may also use: 8.31 kPA(L)/mol(K) or 62.4 Torr(L)/mol(K).

Temperature must always be in Kelvin (K) to avoid using 0 C and getting no solution when students divide.

There is a variation of the ideal gas law that uses the density of the gas with the equation PM = dRT.

Where M is the Molar Mass in g/mol and d is the Density of the gas in g/L.?

Pressure and Temperature must remain in the units atm and K and the Gas Law Constant remains R = 0.0821 (atm) L / (mol) K.

If a 100 g of nitrogen gas compressed in a rigid container at 1.5 atm and 25 C What volume should the container be?

P = 1.5 atm
V = ?
n = 100 g / 28g = 3.57 moles (28 g is the mass of Nitrogen gas ${N}_{2}$
R = 0.0821 atm L / mol K
T = 25 C + 273 = 298K

PV =nRT becomes V = nRT/P

V = 3.57 mol (0.0821 atm L /mol K) (298 K / 1.5 atm

V = 58.2 L

Notice the gas law constant allows to cancel all the units except the liters (L).

I know this was long, but I hope it is helpful
SMARTERTEACHER