A sample of hydrogen gas occupies a volume of 33.4 L at STP. How many moles of hydrogen gas is this?

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Feb 9, 2018

I got #"1.47 mols"#....


If we ASSUME (!!!!) that hydrogen gas is an ideal gas, then we ASSUME that the ideal gas law works:

#PV = nRT#

  • #P# is pressure in #"atm"# or #"bar"#...
  • #V# is volume in #"L"#.
  • #R = "0.083145 L"cdot"bar/mol"cdot"K"# #=# #"0.082057 L"cdot"atm/mol"cdot"K"# is the universal gas constant.
  • #T# is the temperature in #"K"#.
  • #n# is obviously the mols of IDEAL gas.

And so,

#n = (PV)/(RT)#

STP is defined since 1982 as #0^@ "C"# and #"1 bar"#. STP is defined before 1982 as #0^@ "C"# and #"1 atm"#.

Before 1982,

#n = ("1 atm"cdot"33.4 L")/("0.082057 L"cdot"atm/mol"cdot"K" cdot "273.15 K")#

#=# #"1.49 mols"#

But since we're not old-timers who are stuck in the past, we look at AFTER 1982 to obtain:

#n = ("1 bar" cdot "33.4 L")/("0.083145 L"cdot"bar/mol"cdot"K" cdot "273.15 K")#

#=# #ulcolor(blue)"1.47 mols"#

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Feb 9, 2018

At STP, all gases have a molar volume of 22.4 L/mol
#(33.4 L)((1mol)/(22.4 L))= 1.49 mol#

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