1. Stoichiometry of Gases
Section 11.3
Stoichiometry of Gases

2. Introduction to Gas Stoich.
Stoichiometry is used when a given amount of a substance is used to determine the amount of another substance reacting or produced in a given reaction.
What represents the mole ratio in a balanced equation? What is the significance of the mole ratio?
2 Na + __ Cl2  2 NaCl
__ CH O2  __ CO H2O
What does Avogadro’s Principle state?
Equal volumes of gases at the same temperature and pressure contain equal numbers of particles.
Assuming that both substances exist under the same conditions, the unknown substance’s (volume, mass, number of particles, or amount in moles) can be determined.

3. Steps for Solving: Write the balanced equation.
Identify the given and the unknown.
Check to see if the gas conditions are at STP.
If at STP go to Step 5. If not at STP go to Step 6.
If the conditions are standard, apply Avogadro’s Principle along with regular stoichiometry to solve for the unknown substance in the appropriate unit.
If not at STP you must use the Ideal Gas Law equation along with regular stoichiometry to solve for the unknown substance in the appropriate unit.
What is the Ideal Gas Law equation?
PV = nRT

4. Examples:
Assuming all volume measurements are made at the same temperature and pressure (STP), what volume of hydrogen gas is needed to react completely with 4.55 L of oxygen gas to produce water vapor? Equation: ____ H ___ O2  ___ H2O
How many grams of Calcium carbonate must be decomposed to produce 5.00 L of Carbon dioxide gas at STP? Equation: _____ CaCO3  _____ CaO + _____ CO2 2 2
4.55 𝐿 𝑂2 𝑥 2 𝑣𝑜𝑙 𝐻2 1 𝑣𝑜𝑙 𝑂2 = 9.10 L H2
5.00 𝐿 𝐶𝑂2 𝑥 1 𝑣𝑜𝑙 𝐶𝑎𝐶𝑂3 1 𝑣𝑜𝑙 𝐶𝑂2 = 5.o0 L CaCO3
5.00 𝐿 𝐶𝑎𝐶𝑂3 𝑥 1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂 𝐿 𝐶𝑎𝐶𝑂3 𝑥 𝑔 𝐶𝑎𝐶𝑂3 1 𝑚𝑜𝑙 𝐶𝑎𝐶𝑂3 =22.5𝑔 𝐶𝑎𝐶𝑂3

5. More Examples: 3 3 2 2 PV = nRT V = 292 L PV = nRT V = 3.54 L
How many liters of hydrogen gas at 35 oC and atm are needed to react completely with 875 g of tungsten oxide? Equation: ___ WO ___ H2  ___ W + ___ H2O
What volume of chlorine gas at 38 oC and 1.63 atm is needed to react completely with 10.4 g of sodium to form NaCl? Equation: _____ Na _____Cl2  _____ NaCl
PV = nRT 3 3
P = atm
V = ?
n = mol
R =
T = 308 K
(0.980)(V) = ( )(0.0821)(308)
875 𝑔 𝑊𝑂3 𝑥 1 𝑚𝑜𝑙 𝑊𝑂 𝑔 𝑊𝑂3 𝑥 3 𝑚𝑜𝑙 𝐻2 1 𝑚𝑜𝑙 𝑊𝑂3 = 𝑚𝑜𝑙 𝐻2
V = 292 L
PV = nRT 2 2
P = 1.63 atm
V = ?
n = mol
R =
T = 311 K
(1.63)(V) = (0.2262)(0.0821)(311)
10.4 𝑔 𝑁𝑎 𝑥 1 𝑚𝑜𝑙 𝑁𝑎 𝑔 𝑁𝑎 𝑥 1 𝑚𝑜𝑙 𝐶𝑙2 2 𝑚𝑜𝑙 𝑁𝑎 = 𝑚𝑜𝑙 𝐶𝑙2
V = 3.54 L