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Section 2
Avogadro’s Law (5.2)
Ideal Gas Law (5.3)
Gas Stoichiometry (5.4)
Chemistry- Unit 7
• volumes of gas at the same temperature
and pressure contain equal number of
molecules
Volume & Amount
Avogadro’s Law
k is a constant for that specific gas
V = kn
Volume & Amount
Avogadro’s Law
• For 1 mole of an ideal gas at 0°C and 1 atm,
the volume of the gas is 22.42 L.
• 1 mol gas = 22.4 L gas (@ STP)
• STP = standard temperature and pressure
0°C and 1 atm
Therefore, the molar volume is 22.42 L at STP.
If 2.45 mol of argon gas occupies a volume
of 89.0 L, what volume will 2.10 mol of
argon occupy under the same conditions of
temperature and pressure?
76.3 L
Concept Check
• mathematical relationship between
pressure, volume, temperature and
amount of a gas
• We can bring all of these laws together
into one comprehensive law:
Ideal Gas Law
PV= k
T
V = knPV
≈ knT
R = 0.0821 L·atm/mol·K (the universal gas constant)
Ideal Gas Law
PV≈ kn
T
PV= Rn
TPV = nRT
Ideal Gas Law
• For 1 mole of an ideal gas at 0°C and 1
atm, the volume of the gas is 22.42 L.
• STP = standard temperature and pressure
0°C and 1 atm
Therefore, the molar volume is 22.42 L
at STP.
Molar Volume of an Ideal Gas
An automobile tire at 23.0°C with an internal
volume of 25.0 L is filled with air to a total
pressure of 3.18 atm. Determine the
number of moles of air in the tire.
3.27 mol
Concept Check
What is the pressure in a 304.0 L tank that
contains 5.670 kg of helium at 25.00°C?
114 atm
Concept Check
At what temperature (in °C) does 121 mL of
CO2 at 27°C and 1.05 atm occupy a volume
of 293 mL at a pressure of 1.40 atm?
696°C
Concept Check
A sample of oxygen gas has a volume of
2.50 L at STP. How many grams of O2 are
present?
3.57 g
Concept Check
Consider the following reaction:
4Al(s) + 3O2(g) → 2Al2O3(s)
It takes 2.00L pure oxygen gas at STP to
react completely with a certain sample of
aluminum. What is the mass of aluminum
reacted?
3.21 g Al
Concept Check
Ideal Gas Law Summary
PV = nRT
PV = nRT P1V1 = P2V2
PV = nRT
V nR=
T P
V1 V2
= T1 T2
If temp and amount stay constant…
If P and n stay constant…
Rearrange for V & T
Ideal Gas Law
Boyle’s Law
Charles’ Law
Ideal Gas Law Summary
PV = nRT
PV = nRT
PV = nRT
P nR=
T V
P1 P2
= T1 T2
PV= nR
T
P1V1 P2V2
= T1 T2
If V and n stay constant…Rearrange for P & T
Rearrange for P, V & T
If n stays constant…
Ideal Gas Law
Gay-Lussac’s Law
Combined Gas Law
Ideal Gas Law Summary
PV = nRT
P1 P2
= T1 T2
P1V1 P2V2
= T1 T2
By knowing the Ideal Gas Law, you can
determine all other equations needed.
V1 V2
= T1 T2
P1V1 = P2V2
A sample of methane gas (CH4) having a
volume of 2.80L at 25oC and 1.65atm was
mixed with a sample of oxygen gas having
a volume of 35.0L at 31oC and 1.25atm.
The mixture was then ignited to form carbon
dioxide and water. Calculate the volume of
CO2 formed at a pressure of 2.50atm and a
temperature of 125oC.
2.47 L
Concept Check
Molar Mass of a Gas
• Molar mass (M)
• grams per molem
M =n
mn =
MRearrange for n
PV = nRT ormRT
PV = M
mRTM =
PVSubstitute for n Rearrange for M
(if needed)
At 18oC and 765torr, 2290mL of a gas
weighs 3.71grams. Calculate the molecular
mass of the gas?
38.3 g/mol
Concept Check
Density of a Gas
• Mass per volume
mD =
V
Starting with the equation for Molar Mass
mRTM =
PV
DRTM =
P
MPD =
RTSubstitute for m/V Rearrange for D
(if needed)
What is the density of F2 at STP (in g/L)?
1.70 g/L
Concept Check
The volume of a quantity of sulfur dioxide at
18oC and 1500torr is 4.3L. Calculate its
volume at STP?
8.0L
Concept Check
If a gas occupies 3.00L at STP, what
volume will it occupy at 300oC and 25atm?
0.25L
Concept Check
Calcium metal reacts with hydrochloric acid
to yield hydrogen and calcium chloride.
Determine the volume of hydrogen gas at
1.00atm and 18oC produced from the
reaction of 12.2g of calcium with excess
hydrochloric acid.
7.27L H2
Concept Check
A volume of 95cm3 of nitrous oxide at 27oC
is collected over mercury in a graduated
tube, the level of mercury inside the tube
being 40mm above the outside mercury
level when the barometer reads 750torr.
Compute the volume of the same mass of
gas at STP.
.81L = 810mL
Concept Check
Recommendations
• List out the variables.
– Convert all variables that need conversion.
• Ask: It is “a before and after” or is it
“a snapshot.”
• Start with Ideal Gas Law then convert to
needed equation.
• Solve.
Gas Laws Review
Section 2Homework Set
Chemistry- Unit 7
pg 225 #43, 44, 45, 46, 49, 50,
65, 66, 71, 75, 77
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