How do you solve gas laws problems with the given "at STP" and with mass?

1 Answer
Jan 15, 2017

Answer:

I like to use the Ideal Gas Law.

Explanation:

The Ideal Gas Law is:

#color(blue)(bar(ul(|color(white)(a/a)PV = nRTcolor(white)(a/a)|)))" "#

where

  • #P# is the pressure
  • #V# is the volume
  • #n# is the number of moles
  • #R# is the universal gas constant
  • #T# is the temperature

We can rearrange the Ideal Gas Law to get

#V = (nRT)/P#

Also,

#"Moles" = "mass"/"molar mass" = m/M#

#V = (m/M) (RT)/P = (mRT)/(PM)#

EXAMPLE

What is the volume of 10.0 g of hydrogen at STP?

Solution

Remember that STP is defined as 0 °C and 1 bar.

#m = "10.0 g"#
#R = "0.083 14 bar·L·K"^"-1""mol"^"-1"#
#T = "(0 + 273.15) K" = "273.15 K"#
#P = "1 bar"#
#M = "2.016 g·mol"^"-1"#

#V = (mRT)/(PM) = (10.0 color(red)(cancel(color(black)("g"))) × "0.083 14" color(red)(cancel(color(black)("bar"))) ·"L"· color(red)(cancel(color(black)("K"^"-1""mol"^"-1"))) × 273.15 color(red)(cancel(color(black)("K"))))/(1 color(red)(cancel(color(black)("bar"))) × 2.016 color(red)(cancel(color(black)("g·mol"^"-1")))) = "113 L"#