1. Ch. 13 – Gases
Gas Stoichiometry

2. * Stoichiometry Steps Review *
1. Write a balanced equation.
2. Identify known & unknown.
3. Line up conversion factors.
Mole ratio - moles  moles
Molar mass – moles  grams
Molar volume – moles  liters gas
Molarity – moles  liters soln
Mole ratio – moles  moles
Core step in all stoichiometry problems!!
4. Check answer.

3. Standard Temperature & Pressure
* Molar Volume at STP
1 mol of a gas=22.4 L
at STP
Standard Temperature & Pressure
0°C and 1 atm

4. * Stoichiometry Conversions
LITERS
OF GAS
AT STP
Molar Volume
(22.4 L/mol)
MASS IN
GRAMS
MOLES
NUMBER OF
PARTICLES
Molar Mass
(g/mol)
6.022  1023
particles/mol

5. A. Gas Stoichiometry – Volume
Liters of known gas  Liters of an unknown gas:
Avogadro’s Principle
Equal volumes of gases contain equal numbers of moles
Coefficients give mole ratios and volume ratios

6. A. Gas Stoichiometry – Volume
What volume of oxygen is needed for the complete combustion of 4.00 L of propane (C3H8)?
C3H O2  CO2+ H2O
4.00 L ?L
4.00 L
C3H8
5 L O2
1 L
C3H8
= 20.0 L O2

7. B. Gas Stoichiometry – STP
Moles or grams of one substance  Liters of a Gas:
Pressure and temperature will change the volume of a gas, so these need to be known to calculate amounts of reactants needed and products produced
STP – use 22.4 L/mol

8. B. Gas Stoichiometry Problem – STP
How many grams of KClO3 are req’d to produce 9.00 L of O2 at STP?
2KClO3  2KCl + 3O2
? g
9.00 L
9.00 L O2
1 mol O2
22.4 L
2 mol
KClO3
3 mol O2
122.55
g KClO3
1 mol
KClO3
= 32.8 g
KClO3

9. C. Gas Stoichiometry – Non-STP
Given liters of gas?
start with ideal gas law
Looking for liters of gas?
start with stoichiometry conversion

10. C. Gas Stoichiometry Problem – Non-STP
How many grams of Al2O3 are formed from L of O2 at 97.3 kPa & 21°C? 1
4 Al(s) O2(g)  2 Al2O3(s)
15.0 L
non-STP
? g
GIVEN:
P = 97.3 kPa
V = 15.0 L
n = ?
T = 21°C = 294 K
R = LkPa/molK
WORK:
PV = nRT
(97.3 kPa) (15.0 L) = n (8.315 LkPa/molK) (294K)
n = mol O2
Given liters: Start with Ideal Gas Law and calculate moles of O2.
NEXT 

11. C. Gas Stoichiometry Problem – Non-STP
How many grams of Al2O3 are formed from 15.0 L of O2 at 97.3 kPa & 21°C? 1
4 Al(s) O2(g)  2 Al2O3(s)
15.0L
non-STP
? g
Use stoich to convert moles of O2 to grams Al2O3
0.597
mol O2
2 mol Al2O3
3 mol O2
g Al2O3
1 mol
Al2O3
= 40.6 g Al2O3

12. C. Gas Stoichiometry Problem – Non-STP
What volume of CO2 forms from g of CaCO3 at 103 kPa & 25ºC? 2
CaCO3(s)  CaO(s) CO2 (g)
5.25 g
? L non-STP
Looking for liters: Start with stoich and calculate moles of CO2.
P = 103 kPa
V = ?
n = ?
R = dm3kPa/molK
T = 298K
5.25 g
CaCO3
1 mol
CaCO3
100.09g
1 mol
CO2
CaCO3
NEXT 
= mol CO2
Plug this into the Ideal Gas Law for n to find liters

13. C. Gas Stoichiometry Problem – Non-STP
What volume of CO2 forms from g of CaCO3 at 103 kPa & 25ºC? 2
GIVEN:
P = 103 kPa
V = ?
n = mol
T = 25°C = 298 K
R = LkPa/molK
WORK:
PV = nRT
(103 kPa)V =( mol)(8.315 LkPa/molK) (298K)
V = 1.26 L CO2