1. Gas Volumes and Ideal Gas Law
11-3

2. 11-3 Learning Targets
Relate the number of particles and volume by using Avogadro’s principle
Define Standard Molar volume of Gas
Determine volume ratios for gaseous reactants and products using coefficients from a chemical equation
Relate the amount of gas present to its pressure, temperature and volume by using the ideal gas law

3. Gay-Lussac’s Law of Combining volumes of gases
At constant temperature and pressure, the volume of gaseous reactants and products can be expressed as ratios of small whole numbers
H2 gas+ Cl2 gas → 2HCl gas
1 L L = 2L
1 vol 1 vol = 2 vol

4. Avogadro’s Law Italian Amadeo Avogadro
Equal volumes of gases at the same temp and pressure contain equal number of molecules
Volume varies directly with number of molecules
V = k n
Avagadro’s Law V1 = V2
n n2
constant T and P

5. Avogadro's Law Problem
Suppose we have 12.2 L sample of mol Oxygen gas O2 at 1 atm and 25 °C. If all of this gas is converted to ozone,O3 , at the same temperature and pressure, what will be the volume of the ozone formed?
3O2→2 O3
.5 mol O2 x 2 mol O3 = .33 mol O3
3 mol O2
12.2 L = V2
0.50 mol O mol O3
V2 = 8.1 L O3

6. Avogadro's Law Problem
1.5 mol N2 has a volume of 36.7 L. It is at 25 °C and 1 atm. If the temperature and pressure is held constant how many moles will have a volume of 16.5 L?
36.7 L = L
1.5 mol N n2
n2= mol N2

7. Standard Molar Volume of Gas
Volume occupied by one mole of gas at STP = L
22.4 L/mol
If know volume of gas can use 1 mol/ 22.4 L as conversion factor to find moles (then mass) of a given volume of gas at STP

8. Problem At STP, what is the volume of 9.02 mol of oxygen gas?
9.02 mol O2 x (22.4 L/mol) = 202 L O2
A sample of H2 occupies 4.3 L at STP. How many moles of the gas are present?
4.3 L H2 x ( 1 mol/ 22.4L)= mol H2

9. Gas Stoichiometry
Volume- Volume calculations- use volume ratios like mole ratios
MUST HAVE BALANCED EQUATION!!!!

10. What volume of hydrogen gas is needed to react completely with 10
What volume of hydrogen gas is needed to react completely with 10.5 L of oxygen gas to produce water vapor?
2H2 + O2 →2 H2O 10.5L O2 (2 LH2 ) = 21.0 L H2 1 L O2

11. Gas Stoichiometry Volume-mass calculations
Volume A to moles A to moles B to mass B
Mass-volume calculations
Opposite direction as above

12. Mass to Volume
Calculate the volume of CO2 produced at STP from the decomposition of 152 g of CaCO3 according to the reaction.
CaCO3 (s) → CaO + CO2
Convert g to moles
152g CaCO3 x 1 mole CaCO3 = 1.52 mol CaCO3 g
1to 1 mole ratio
1.52 mol CO2 x L CO2 = 34.1 L CO2
1 mol CO2
Can only use molar volume because at STP

13. Volume to Mass
How many grams of calcium carbonate must be decomposed to produce 5.00 L of carbon dioxide gas at STP?
CaCO3 (s) → CaO + CO2
1to 1 ratio , 1 L of CaCO3 to 1L of CO2
5.0 L CaCO3 (1 mol = mol CaCO3
22.4 L)
0.2232mol CaCO3 ( g
1mol) = 22.34g CaCO3

14. Ideal Gas Law Combine all gas laws (Boyle, Charles, and Avogadro)
Mathematical relationship of pressure, volume, temperature, number of moles
Ideal gas- follows KMT
pressure not too high and temperature not too low
around a temp of 0 °C or higher
Pressure around 1 atm or lower

15. Ideal Gas Law PV= nRT P= pressure V= volume (L)
T= temp (K) n = number of moles
R= Ideal gas constant
Make sure units in problem match units in R

16. R= gas constant R= 0.0821 L∙ atm mol∙ K R= 62.4 L∙ mmHg
R= L∙ kPa

17. Nitrogen gas has a volume of 1
Nitrogen gas has a volume of 1.75 L at STP, how many moles of the gas are present?
PV=nRT
n=PV RT
n= (1 atm)(1.75L)
( L∙atm/K∙mol)( 273K)
= mol N2

18. How many grams of carbon dioxide must be decomposed to produce 5
How many grams of carbon dioxide must be decomposed to produce 5.00 L of carbon dioxide gas at STP?
Ideal gas law PV=nRT
(1.00 atm)(5.00 L CO2) = n L∙ atm /mol K (273K)
= mol CO2
0.223 mol CO2 (43.99 g CO2 ) = mol CO2
= 9.81g CO2