The molar volume is the volume occupied by one mole of ideal gas at STP. Its value is:
22.414 L mol¯1
It is actually known to several more decimal places but the number above should prove sufficient.This value has been known for about 200 years and it is not a constant of nature like, say, the charge on the electron. If we had picked a diffeent standard temperature, then the molar volume would be different.
Using PV = nRT, you can calculate the value for molar volume. V is the unknown and n = 1.00 mol. Set P and T to their standard values and use R = 0.08206.
Molar volume doesn't show up that often in problems. As a consequence, teachers sometimes like to use molar volume on the test, in order to trip the kid up!! Let's do some examples.
Example #1: you have 2.00 L of dry H2 at STP. How many moles is this?
Solution: we could solve this with PV = nRT, but we can shortcut since we have STP and do this:
Example #2: 0.250 moles of HCl will occupy how many liters at STP?
Solution: this is just the reverse of example one:
0.250 mol x 22.414 L mol¯1
Example #3: What is molar volume at 576 K?
Solution: strictly speaking, this isn't more than a volume-temperature problem, but for some reason putting "molar volume" in the problem messes people up.
22.414 L mol¯1 / 273 K = x / 546 K
Notice that 546 is double 273, so that just confims the answer of 44.828 L.