Name______________________________
Honors Chemistry Classnotes and Practice Problems
Ideal Gas Law
Avogadro’s Principle - Equal volumes of gases contain the SAME number of particles
Molar volume of a gas – volume that 1 mol occupies at STP (273K and 1 atm)
What is that volume??? __22.4 L_________
Ideal Gas Constant
Combined Gas law - plug in values from warm up and see if both sides are equal…
P1V1 = P2V2  __0.0821 = 0.0821_______
T1
T2
For a specific sample of gas – relationship between pressure, volume, and temp is ALWAYS the
same PV = _R = 0.0821 L atm/mol K______
T
Deriving the Ideal Gas Law:
Use the combined gas law and gas constant R, add in moles and…..
PV = R rearranges to PV = nRT
nT
In Class Practice:
Calculate the number of moles of ammonia gas (NH3) contained in a 3.0 L vessel at 300 K and
1.50 atm of pressure.
Your turn:
Determine the temperature (in °C) of 2.49 mol of a gas contained in a 1.0 L vessel at 143 kPa.
(Remember that because of R, your calculations have to be in Kelvin and atm!)
Name______________________________
Honors Chemistry Classnotes and Practice Problems
Finding Molar Mass
You can use the ideal gas law to find the molar mass of an unknown gas!
Remember:
moles (n) =
mass (g)
molar mass (g/mol)
So we can replace n with m/MM in PV = nRT
PV = mRT
MM
which rearranges to MM = mRT
PV
Substituting with Density
Since MM = mRT , and we know that D = m/v
PV
How can we use density to find MM?
MM =
DRT
P
In summary,
PV = nRT and since n = m/MM then MM = mRT/PV
AND since d = m/v, now MM = DRT/P!
In class practice:
What is the molar mass of gerinol (a compound found in perfumes) if its vapor has a density of
0.480 g/L at a temperature of 260 °C and a pressure of 0.140 atm?
Your turn:
1. Rearrange MM= DRT/P to solve for D :
2. Determine the density of chlorine gas at 295K and 1 atm.
Name______________________________
Honors Chemistry Classnotes and Practice Problems
Deviations of REAL gases
Remember that the IDEAL gas law assumes that all gases behave ideally as described by kinetic
molecular theory.
Gas particles are tiny
Gases experience no intermolecular attractions
Collisions of gas particles are perfectly elastic and do not lose energy.
REAL gases are not really IDEAL
• Gas particles are small but do take up volume.
• Gases do experience some intermolecular attractions
• Collisions are not perfectly elastic and some energy is lost.
BUT
• Most gases behave similarly to ideal so we can still use the ideal gas law to approximate
them!
Factors For Non-Ideal Behavior
Gases cannot be approximated accurately by the ideal gas law at
really HIGH PRESSURE and really LOW TEMPERATURE
Why? (Consider IMF’s and phases)
Gases are less ideal when:
A gas is HIGHLY POLAR or has LARGE PARTICLES
Why?
Name______________________________
Honors Chemistry Classnotes and Practice Problems
Ideal Gas Law
_____________ Principle - _______ volumes of gases contain the ______ number of particles.
Molar volume of a gas – volume that 1 mol occupies at STP (273K and 1 atm)
What is that volume??? ______
Ideal Gas Constant
Combined Gas law - plug in values from warm up and see if both sides are equal…
P1V1 = P2V2  ______
T1
T2
For a specific sample of gas – relationship between pressure, volume, and temp is _________
the same PV = __________________
T
Deriving the Ideal Gas Law:
Use the combined gas law and gas constant ___, add in _________ and…..
= R rearranges to PV =
In Class Practice:
Calculate the number of moles of ammonia gas (NH3) contained in a 3.0 L vessel at 300 K and
1.50 atm of pressure.
Your turn:
Determine the temperature (in °C) of 2.49 mol of a gas contained in a 1.0 L vessel at 143 kPa.
(Remember that because of R, your calculations have to be in Kelvin and atm!)
Name______________________________
Honors Chemistry Classnotes and Practice Problems
Finding Molar Mass
You can use the ideal gas law to find the molar mass of an unknown gas!
Remember:
moles (n) =
So we can replace ___ with _________ in PV = nRT
PV =
Since MM =
which rearranges to MM =
Substituting with Density
, and we know that D =
How can we use density to find MM?
MM =
In summary,
PV = ______ and since n = _________ then MM = _____________
AND since d = _________, now MM = __________!
In class practice:
What is the molar mass of gerinol (a compound found in perfumes) if its vapor has a density of
0.480 g/L at a temperature of 260 °C and a pressure of 0.140 atm?
Your turn:
1. Rearrange MM= DRT/P to solve for D :
2. Determine the density of chlorine gas at 295K and 1 atm.
Name______________________________
Honors Chemistry Classnotes and Practice Problems
Deviations of REAL gases
Remember that the IDEAL gas law assumes that all gases behave ideally as described by kinetic
molecular theory.
Gas particles are ________
Gases experience no _______________________
Collisions of gas particles are perfectly ___________ and do not lose ________.
REAL gases are not really IDEAL
• Gas particles are small but _________________________.
• Gases do experience _______________________________.
• Collisions are not perfectly elastic and ____________________________.
BUT
• Most gases behave ____________ to ideal so we can still use the ideal gas law to
_____________________ their properties!
Factors Contributing to Non-Ideal Behavior
Gases cannot be approximated accurately by the ideal gas law at
really __________________ and really ______________________
Why? (Consider IMF’s and phases)
Gases are less ideal when:
A gas is _______________________ or has ______________________
Why?
Name______________________________
Honors Chemistry Classnotes and Practice Problems
Practice Problems:
1. Calculate the volume that 0.540 mol of propane occupies at STP.
2. A 2 L flask is filled with propane gas (C3H8) at a pressure of 1 atm and a temperature of -15
°C. What is the mass of propane in the tank?
3. Calculate the number of moles of oxygen gas held in a 2 L tank at 3.5 atm and 298 K.
4. How many moles would be in the tank if the temperature was raised to 49 °C and the
pressure remained constant?
5. Find the volume that 42 g of carbon monoxide gas occupies at STP.
6. A 2.5 L flask is filled with ethane gas (C2H6) at a pressure of 1.08 atm and temp of 15 °C. What
is the mass of ethane in the flask?
7. How many moles of helium gas would be required to fill a 22 L container at 35 °C and 3.1
atm?
8. At what temperature would 2.10 moles of nitrogen gas have a pressure of 1.25 atm and in a
25.0 L tank?
9. What is the density of radon gas at STP?
10. What is the density of methane, CH4, at STP?
11. Calculate the molar mass of a gas whose density is 1.25 g/L at STP?
12. 2.94 grams of a gas exert a pressure of 0.284 atm in a 3.60 L container at 265 oC. Calculate
the molar mass of the gas.
13. Find the density of butane, C4H10, at 22oC and 0.961 atm.
14. A 250.0 mL sample of a noble gas collect at 88.1 kPa and 7°C has a mass of 0.378 g. What is
the molar mass of the gas? Identify the sample.
15. Determine the volume of 12.3 g of formaldehyde gas (CH2O) at STP?
Also book problems Ch 13 – 92, 93, 94, 96