In a chemical reaction you collect 1L Hydrogen gas at STP. How many moles of hydrogen gas did you collect?

In this question, we're given:

• #p#, or pressure, of #"1 atm"#. We know this because it tells us that we're at STP.
• #V#, or volume, of #"1 L"#.
• #T#, or temperature, at #"273.15 K"#. We know this because it tells us that we're at STP.

We need to find #n#, or number of moles.
The Ideal Gas Equation relates all of these variables!:

#pV = nRT#

We can rearrange this to only have #n# on one side:

#n = (pV)/(RT)#

We know the value of #R#, or the Universal Gas Constant, to be #"0.08206 L atm/K mol"# because the units for our given values are in #"L"#, #"atm"#, and #"K"#.
Now, we can just plug in the variables and solve:

#n = ("1 atm" xx "1 L")/("0.08206 L atm/K mol" xx "273.15 K")#
#n = (1 cancel("atm") xx 1 cancel("L"))/(0.08206 cancel("L") cancel("atm")"/"cancel("K") "mol" xx 273.15 cancel("K"))#
#n = "0.0446 mol"#

We can verify that our answer is correct by plugging everything into the Ideal Gas Equation again and seeing if #pV# is really equal to #nRT#:

#pV = nRT#
#"1 atm" xx "1 L" = "0.0446 mol" xx "0.08206 L atm/K mol" xx "273.15 K"#
#1 = 1#

Yay! :)