The Ideal Gas Law
PV=nRT
P = Pressure
V = Volume
 n = Number of Moles
R = ideal gas constant
T = temperature in Kelvin
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R -The ideal gas constant
Depends on unit of pressure
0.0821 L . Atm / K . mol
62.4 L . mmHg / K . mol
8.31 L . kPa / K . mol
Ideal Gas Law
example problem
 Calculate the pressure of 1.65 g of helium gas at
16.0oC and occupying a volume of 3.25 L?
 You will need g to moles and Celsius to Kelvin:
 1.65 g He 1 mole He

4.0 g He = 0.412 mol He
 K = oC + 273 ; 16. 0 + 273 = 289 K
 For this problem you will need to pick an R value. For
this problem I will choose to use the R value
containing kPa. I picked it. You can’t do anything
about it. So; just try and stop me.
 Plug and Chug baby, get ‘R done. Do it. Come on I
dare ya.
Ideal Gas Law
example problem
 P x 3.25 L = 0.412 mol x 8.31 kPa . L x 289 K

mol . K
 Do the algebra and solve; if you do it right, guess
what? You get the answer right. Neat concept, huh?
 = 304 kPa
 Your turn
 How many moles of gas are present in a sample of
Argon at 58oC with a volume of 275 mL and a
pressure of 0.987 atm.
Ideal Gas Law
example problem
 Answer
 0.987 atm x 0.275 L = n x 0.0821 L . Atm x 331K

mol . K
 Do the dew; oops, I mean the algebra and presto;
the answer with the correct number of sig figs is..
 Do you know how to keep a so called chem student
in suspense?
 Do ya?
 = 0.00999 mol Ar
 Congrats - you can plug and chug.
 Bye Bye now.