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Wize University Chemistry Textbook > Gases and their Properties

Gas Mixtures & Partial Pressures

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Gas Mixtures & Partial Pressures

When dealing with mixtures of gases, the total pressure of the gases is equal to the sum of the partial pressure of each component.



Dalton’s Law of Partial Pressures:

PTotal=P1+P2+P3...=ΣPi\boxed{P_{Total}=P_1+P_2+P_3...=\Sigma P_i}

PTotal is the single measured pressure of the mixture
P1 is the partial pressure of gas 1, and so on

Partial pressure: is the pressure that would be exerted by one of the gases in the mixture if it occupied the same volume on its own.

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Note: The total pressure depends on the total number of moles (not on the identity of the gases)

PV=nRTPV=nRT

Ptotal=ntotalRTVP_{total}=\frac{n_{total}RT}{V}


We can also relate the partial pressure of an individual gas (ex. Gas "A") to the total pressure by the mole fraction (X) of that gas.
The mole fraction (X) is a proportion of that gas.

PA=nAnTotalPTotal=XAPTotal\boxed{P_A=\frac{n_A}{n_{Total}}P_{Total}=X_AP_{Total}}

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Example: Partial Pressures

If we have a container with 75% nitrogen, 20% oxygen, and 0.04% carbon dioxide, the total pressure in the container is measured to be 760 Torr (recall this is equal to 1 atm!). What is the partial pressure of oxygen gas? (Ans in torr)

PiO2= XPT
=0.2(760 torr)
=152 torr

Practice: Partial Pressures

A vessel contains He, Ne, and Ar gas. There's twice as much He as Ne and half as much Ar as He. The total pressure in the vessel is 400torr. What is the partial pressure of Ar(g)?

Practice: Partial Pressures

Two gases were mixed together in a 5 L vessel at 243 K to create a total pressure of 9.3 atm. If gas 1 has 2 moles, what is the partial pressure of gas 2? (R = 0.08206 L*atm/mole*K)
Extra Practice
Ideal Gas Law: Kinetic Molecular Theory
The natural gas delivered to homes in Calgary is normally a mixture of methane (CH4), ethane (C2H6), propane (C3H8) and carbon dioxide (CO2).
(a) In the laboratory, a chemistry student has collected some Calgarian natural gas in a 2.00 L plastic bottle at 0.902 atm and 23°C. What is the concentration of gas in the bottle?
(b) The bottle was weighed before and after filling with gas to determine the exact composition of gases. The student found that in the mixture the mole fraction of C3H8(g) was 0.10 and the mole fraction of CH4(g) was 0.90. What was the total mass of the gas in the bottle?
Partial Pressure and Vapor Pressure
A sample of N2 gas was collected over water. The temperature of the vessel was 300.0 K and the volume of the sample was 18.0 L. The vapor pressure of water at 300.0 K is 3.53 kPa and the total pressure of the sample was 122.00 kPa. What is the mass of the N2 in this sample?
Ideal Gas Law: Gas mixtures
When 100 g of Kr and 100 g of Xe are placed in a container, the partial pressure of Xe is found to be 4 atm. What is the partial pressure of Kr?
Practice: Kinetic Molecular Theory
The natural gas delivered to homes in Calgary is normally a mixture of methane (CH4), ethane (C2H6), propane (C3H8) and carbon dioxide (CO2).
(a) In the laboratory, a CHEM 203 student has collected some Calgarian natural gas in a 2.00 L plastic bottle at 0.902 atm and 23°C. What is the concentration of gas in the bottle?
(b) The bottle was weighed before and after filling with gas to determine the exact composition of gases. The student found that in the mixture the mole fraction of C3H8(g) was 0.10 and the mole fraction of CH4(g) was 0.90. What was the total mass of the gas in the bottle?
Ideal Gas Law
A student has two balloons held at ambient pressure and temperature (1 atm, 298 K), one is 3 L contains Helium, the other is 14 L and contains argon. The student transfers both gasses into a single balloon which is also held at ambient temperature and pressure. What is the density of the gas mixture in the final balloon?
Partial Pressure and Vapor Pressure
A sample of N2 gas was collected over water. The temperature of the vessel was 300.0 K and the volume of the sample was 18.0 L. The vapor pressure of water at 300.0 K is 3.53 kPa and the total pressure of the sample was 122.00 kPa. What is the mass of the N2 in this sample?
A 10.0 L sample of Br2 gas is collected over water at 298 K. If the total pressure of the sample is 180.0 kPa, how many mols of Br2 are present in this sample? The vapor pressure of water at 298 K is 3.17 kPa. [Do NOT include units in your answers]
A mixture of 4.6 mols of H2 gas, 3.1 mols of N2 gas and 2.6 mols of He are stored in a 60.0 L canister at 298 K. What is the partial pressure of each compound?
P
H2
A mixture of gases containing 02, N2 and H2 contains 0.20 mols of N2 in a 12 L sealed vessel. If the total pressure is 188 kPa at 298 K, what is the partial pressure of nitrogen? What is the average molar mass of this mixture? The density of the mixture is 1.52g/L.
Gas Mixture
A 1.0 L flask (A) of Ne (g), at 3.0 atm and a 2.0 L flask (B) of Ar (g), at 5.0 atm, are connected by a tube of negligible volume. (See the figure below.) The valve between the flasks is opened and the gases mix at constant temperature. What is the mole fraction of each gas?
Partial Pressure
A mixture of H2(g) and CO(g) (total mass 4.50 g) occupies a volume of 3.76 L at 298 K and 108 kPa. What is the partial pressure of each gas in this mixture? Calculate the volume percent of H2?
Vapour Pressure
A sample of N2 gas was collected over water. The temperature of the vessel was 300.0 K and the volume of the sample was 18.0 L. The vapour pressure of water at 300.0 K is 3.53 kPa and the total pressure of the sample was 122.00 kPa. What is the mass of the N2 in this sample?
Partial Pressure
300 mL H2 was collected over water at 21 ⁰C and 748 Torr. Vapour pressure of water at 21 ⁰C is 18.65 Torr.
a. How many moles of H2 and water vapour were present in the moist gas mixture?
b. Calculate the mass of the gas after being dried.
Gas Law
Consider the following two containers of gas that are at the same temperature. Which of the following statements comparing these two containers are false and which are true?
Gases: Vapor Pressure
A sample of N2 gas was collected over water. The temperature of the vessel was 300.0 K and the volume of the sample was 18.0 L. The vapour pressure of water at 300.0 K is 3.53 kPa and the total pressure of the sample was 122.00 kPa. What is the mass of the N2 in this sample?
Vapor Pressure
A sample of H2 gas was collected over water. The temperature of the vessel was 273.15 K and the volume of the sample was 20.0 L. The vapour pressure of water at 300.0 K is 5.0atm and the total pressure of the sample was 15.5atm. What is the mass of the H2 in this sample?
Ideal Gas Law: Gas Mixtures
2. A mixture of 4.6 mols of H2 gas, 3.1 mols of N2 gas and 2.6 mols of He are stored in a 60.0 L canister at 255 K. What is the partial pressure of each compound?
P
H2
Ideal Gas Law: Gas Mixtures
3. A 10.0 L sample of Br2 gas is collected over water at 298 K. If the total pressure of the sample is 180.0 kPa, how many mols of Br2 are present in this sample? The vapor pressure of water at 298 K is 3.17 kPa.
Ideal Gas Laws
4. A 16.0 L gas vessel contains 40.0 kPa of He, 15.0 kPa of Ne and 25.0 kPa of Kr. What is the density of this mixture?
Ideal Gas Law: Partial Pressures
Calculate the partial pressure of neon (in atm) in a mixture of 3.1 g of argon, 1.2 g of neon, and 2.4 g of krypton at 0oC in 1.5 L container.
Gas Laws: Partial Pressure
Calculate the partial pressure of O2 (in atm) in air that is 20% O2 by weight and 80% N2 by weight, at a temperature of 0oC and an ambient pressure of 0.95 atm
2 gases were mixed together in a 5 L vessel at 243 K to create a total pressure of 9.3 atm. If gas 1 has 2 moles, what is the partial pressure of gas 2? (R = 0.08206 L*atm/mole*K)
Gas Laws: Partial Pressure
A vessel contains He, Ne, and Ar gas. There's twice as much He as Ne and half as much Ar as He. The total pressure in the vessel is 400torr. What is the partial pressure of Ar(g)?
A mixture of 4.6 moles of H2 gas, 3.1 moles of N2 gas and 2.6 moles of He are stored in a 60.0 L canister at 255 K. What is the partial pressure of each compound? (Write answer in format X.XX atm, i.e. 4.25 atm)
P
H2
2 g of O2, 6.3 g of N2 and 4.1 g of He are mixed together in a sealed flask. What is the mole fraction of each component? (O2 = 16.00 g/mol, N2 = 14.00 g/mol, He = 4.00 g/mol).
A mixture of 4.6 moles of H2 gas, 3.1 moles of N2 gas and 2.6 moles of He are stored in a 60.0 L canister at 298 K. What is the partial pressure of each compound? (Write answer in format X.XX atm, i.e. 4.25 atm)
P
H2
2 g of O2, 6.3 g of N2 and 4.1 g of He are mixed together in a sealed flask. What is the mole fraction of each component? (O2 = 32.00 g/mol, N2 = 28.00 g/mol, He = 4.00 g/mol).
Ideal Gas Laws: Gas mixtures
2 gases were mixed together in a 5 L vessel at 243 K to create a total pressure of 9.3 atm. If gas 1 has 2 moles, what is the partial pressure of gas 2? (R = 0.08206 L*atm/mole*K)
Gas Laws: Partial pressure
A mixture of ideal gases containing 02, F2 and N2 contains 0.20 mols of N2 in a 12 L sealed vessel. If the total pressure is 198 kPa at 298 K, what is the partial pressure of nitrogen? If the density of this mixture is 1.52 g/L, What is the average molar mass of this mixture?
Ideal Gas Law
A 8.0 L sample of Br2 gas is collected over water at 298 K. If the total pressure of the sample is 168.0 kPa, how many moles of Br2 are present in this sample? The vapor pressure of water at 298 K is 3.17 kPa.
Ideal Gas Law: Partial Pressure
A mixture of 4.6 moles of H2 gas, 3.1 moles of N2 gas and 2.6 moles of He are stored in a 60.0 L canister at 255 K. What is the partial pressure of each compound?
P
H2
Ideal Gas Law: Mole fraction
A 10.0 L sample of Br2 gas is collected over water at 298 K. If the total pressure of the sample is 180.0 kPa, how many moles of Br2 are present in this sample? The vapor pressure of water at 298 K is 3.17 kPa.
Ideal Gas Law: Density
A 16.0 L gas vessel contains 40.0 kPa of He, 15.0 kPa of Ne and 25.0 kPa of Kr. What is the density of this mixture?
Ideal Gas Law: Gas mixtures
A container holds a mixture of oxygen, neon, and helium gases. The partial pressures are 150 torr for oxygen, 300 torr for neon, and 450 torr for helium. What is the mole fraction for neon?
Ideal Gas Law: Gas mixtures
A mass of 0.4 g of hydrogen (H2) and 3.2 g of helium (He) are mixed in a rigid 500 mL container. What is the partial pressure of helium when the container is cooled to 77 K?
Gas mixtures: Partial Pressures
You are visiting Hawaii and decide to take your barometer with you. When sitting on the beach you notice that the barometer is reading roughly 1 atm. The next day you take your barometer up to the top of Mauna Kea (roughly 4200m above sea level). You notice that the barometer has dropped and the column of mercury is only 45.6 cm high. The density of mercury is 13.595 g cm-3 and the force of gravity is 9.8 m s-2, what is the atmospheric pressure on top of Mauna Kea? Please report your answer in atm.
A mixture of noble gases contains 1.46 mols of Ne, 0.45 mols of Ar and 0.12 mols of Kr. What is the partial pressure of Kr if the total pressure of this mixture is 60.0 kPa?
A mixture of ideal gases containing O2, F2 and N2 contains 0.20 mols of N2 in a 12 L sealed vessel. If the total pressure is 188 kPa at 298 K, what is the partial pressure of nitrogen?
Gas Mixtures: Partial Pressures
Consider the reaction of sodium peroxide (Na2O2) to eliminate carbon dioxide (CO2) build-up in airtight spaces such as submarines, shown in this balanced chemical equation:
2Na2O2(s)+2CO2(g)→2Na2CO3(s)+O2(g)2Na_2O_2(s)+2CO_2(g)\to2Na_2CO_3(s)+O_2(g)
If an excess of Na2O2 is added to a rigid flask filled with CO2, how will the total pressure before the reaction (Pinitial) compare to the total pressure after the reaction goes to completion (Pfinal)?
Gas Laws: Mole Fractions and Partial Pressures
Consider a fixed-volume container filled with SO2 (g). To the same container, a researcher now adds N2 (g) gas. How will the mole fraction (χSO2\chi_{SO_2}) and the partial pressure of SO2 (PSO2P_{SO_2})be affected by the addition of this nitrogen gas? Assume constant temperature.
Ideal Gas Law: Kinetic Molecular Theory
The natural gas delivered to homes in Calgary is normally a mixture of methane (CH4), ethane (C2H6), propane (C3H8) and carbon dioxide (CO2).
(a) In the laboratory, a chemistry student has collected some Calgarian natural gas in a 2.00 L plastic bottle at 0.902 atm and 23°C. What is the concentration of gas in the bottle?
(b) The bottle was weighed before and after filling with gas to determine the exact composition of gases. The student found that in the mixture the mole fraction of C3H8(g) was 0.10 and the mole fraction of CH4(g) was 0.90. What was the total mass of the gas in the bottle?
Ideal Gas Law: Mixtures of Gases
You have a rigid container filled with a mixture of three gases: nitrogen, oxygen, and carbon dioxide. Your task is to compare two different methods to remove all of the carbon dioxide from the container.
Method A: Adding a solid material which adsorbs CO2 gas – this means that CO2 molecules stick to this material so that all of the CO2 will be removed when the solid is removed.
Method B: Adding an excess of solid sodium peroxide (Na2O2) to convert all of the CO2 gas to oxygen gas.
Gas Laws: Partial pressure
Consider the reaction shown in this balanced chemical equation:
SiO2(s)+2H2O(g)→SiH4(g)+2O2(g)SiO_2(s)+2H_2O(g)→SiH_4(g)+2O_2 (g)
A rigid flask is filled with 0.20 mol SiO2 (s) and 0.40 mol H2O (g). The initial partial pressure of H2O (g) is 1.0 atm. If the reaction goes to completion and the temperature stays constant, what is the final total pressure in the flask?
Gas Mixtures: Partial pressures
Consider the gas-phase reaction shown in this balanced chemical equation:
2A(g)+B2(g)→2AB(g)2A(g)+B_2(g)→2AB (g)
A rigid flask is filled with gases so that the initial partial pressure of A is 1.0 atm and the intial partial pressure of B is 0.50 atm. If the reaction goes to completion and the temperature stays constant, what is the final pressure in the flask?
Gas mixtures: Partial pressures
Consider the following two containers of gas that are at the same temperature. Which of the following statements comparing these two containers is false?
A 2.5 L flask containing 1.0 atm of gas A is connected to a 0.5 L flask containing 0.75 atm of gas B, after which the valve between the flasks is opened so that the gases can mix and react according to the following reaction equation.
A+3B→AB3A + 3B\rightarrow AB_3
If the theoretical yield is produced at constant temperature, the total pressure in the combined flasks should be....
Like Spring 2019 Exam 2
When 100 g of He and 100 g of Ne are placed in a container, the partial pressure of Ne is found to be 6 atm. What is the partial pressure of He?
Ideal Gas Law: Gas mixtures
When 100 g of Kr and 100 g of Xe are placed in a container, the partial pressure of Xe is found to be 4 atm. What is the partial pressure of Kr?