Untitled - Kelly Walsh High School

Gases 83
Quick Tip
Let’s see how we might use the ideal gas equation. Suppose you want to know
what volume 40.0 g of hydrogen gas would occupy at 37 o C and 0.850 atm? You
have the pressure in atm, you can get the temperature in Kelvin (37 o C 273
310. K), but you will need to convert the grams of hydrogen gas to moles of
hydrogen gas before you can use the ideal gas equation.
Be sure to use the correct molecular mass for those gases that exist as diatomic
molecules—H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2.
First, you’ll convert the 40.0 g to moles:
(40.0 g) (1 mol H 2/2.016 g) 19.84 mol H 2
(We’re not worried about significant figures at this point since this is an intermediate
calculation.)
Now you can rearrange the ideal gas equation for the unknown quantity, the
volume.
PV nRT
V nRT/P
Finally, we enter in the numerical values for the different known quantities:
V (19.84 mol) (0.0821 Latm/Kmol) (310. K) / (0.850 atm)
V 594 L (Rounded to correct significant figures)
5-2 Gas Stoichiometry
We can use the gas law relationships, especially the ideal gas law and the combined
gas law, in reaction stoichiometry problems. For example, suppose you
have 2.50 g of an impure sample of KClO 3 and you want to determine how
many grams of pure KClO 3 are present. You heat the mixture and the KClO 3
decomposes according to the equation:
2 KClO 3(s) l 2 KCl(s) 3 O 2(g)