Molar volume
v2
Dr. Breinan
Chemistry
The molar volume of a gas is simply the volume that one mole occupies. In accordance with
Avogadro’s hypothesis (equal numbers of particles occupy equal volumes at the same
temperature and pressure), this volume is the same for any ideal gas under the same conditions.
At standard conditions (STP, or 1 atm and 0°C) this volume is 22.4 L.
1. A sample of ammonia gas, NH3, occupies 2.50 liters at STP.
(a) How many moles are in this sample?
(b) What is the mass of this sample?
(c) How many ammonia molecules are in this sample (not in moles)?
(d) How many hydrogen atoms are in this sample (not in moles)?
2. A sample of propane gas, C3H8, contains 3.50x1022 molecules at STP.
(a) How many moles are in this sample?
(b) What is the mass of this sample?
(c) What is the volume of the sample?
(d) How many hydrogen atoms are in this sample (not in moles)?
3. A sample of nitrogen gas, N2, has a mass of 25.0 grams at STP.
(a) How many moles of molecules are in this sample?
(b) What is the volume of the sample?
(c) How many nitrogen molecules are in this sample (not in moles)?
(d) How many nitrogen atoms are in this sample (not in moles)?
4. A sample of gas occupies 0.250 L at STP. Its mass is 0.625 grams.
(a) What is the molar mass of the gas?
(b) How many molecules are in this sample (not in moles)?
5. A sample of gas contains 8.50x1021 molecules at STP. Its mass is 1.33 grams.
(a) What is the molar mass of the gas?
(b) What is the volume of the sample?
(c) What will the volume be at 0.965 atm and 298 K?
Answers: 1a) 0.112 mol b) 1.90 g c) 6.74x10 22 d) 2.02x1023
2a) 0.0581 mol b) 2.56 g c) 1.30 L
d) 2.80x1023 3a) 0.893 mol b) 20.0 L c) 5.38x1023 d) 1.08x1024 4) a) 56.0 g/mol b) 6.72x10 21
5) a) 94.2
g/mol b) 0.316 L c) 0.357 L
Gas stoichiometry worksheet
v2
Dr. Breinan
Chemistry
Stoichiometry. Stoichiometry works by the same 5-step method with gases as it did when we
learned it. However, now the mole-it and convert-it steps can involve gas volume! Use 22.4
L/mol at STP, or use the ideal gas law at other conditions to convert between volume and
moles or vice versa. There is also one shortcut for gases... if the conditions (of T and P) are
the same before and after the experiment, the volume ratio is the same as the mole ratio.
R = 0.0821 L•atm / mol•K or 62.4 L•mmHg / mol•K
1. The following reaction occurs at STP: C3H8 (g) + 5 O2 (g) --> 3 CO2 (g) + 4 H2O (g)
If 8.75 L of propane (C3H8 ) are combusted, find...
a) the volume of O2 that reacts
b) the volume of CO2 produced
c) the volume of H2O produced
2. The following reaction occurs at STP: 2 C2H2 (g) + 5 O2 (g) --> 4 CO2 (g) + 2 H2O (g)
If 0.775 mol of carbon dioxide are produced, find...
a) the volume of CO2 produced
b) the volume of O2 that reacts
c) the moles of C2H2 that react
d) the mass of H2O produced
3. The following reaction occurs at STP: 4 NH3 (g) + 5 O2 (g) --> 4 NO (g) + 6 H2O (g)
If 0.671 L of NO is produced, find...
a) the mass of H2O produced
b) the volume of NH3 that reacts
c) the moles of O2 that react
d) the volume of O2 that reacts
4. Given the following reaction: 4 Fe (s) + 3 O2 (g) --> 2 Fe2O3 (s)
a) If 37.5 grams of Fe2O3 is produced, find the moles of Fe that react.
b) If 37.5 grams of Fe2O3 is produced, find the volume of O2 that reacts at STP.
c) If 37.5 grams of Fe2O3 is produced, find the volume of O2 that reacts at 1.1 atm and 25°C.
d) What mass of Fe is needed to react with 13.0 L of oxygen at 733 mmHg and 10°C?
5. How many liters of hydrogen can be produced by reacting 4.0 g of aluminum with excess
hydrochloric acid (a) if the hydrogen is collected at STP; (b) if the hydrogen is collected at
0.92 atm and 30°C?
Answers: 1a) 43.8 L b) 26.3 L c) 35.0 L 2a) 17.4 L b) 21.7 L c) 0.388 mol d) 6.98 g 3a) 0.809 g b)
0.671 L c) 0.0374 mol d) 0.839 L 4a) 0.469 mol b) 7.88 L c) 7.82 L d) 40.2 g
5a) 4.98 L
b) 6.01 L