5.2.2 Partial Pressure and Dalton's Law

Question 1

partial pressure and dalton’s law

Answer 1

• Dalton’s law of partial pressures states that the total pressure of a mixture of gases is the sum of the partial pressures of the individual gases.

Question 2

note

Answer 2

• The partial pressure of a gas is the pressure exerted by that gas in a mixture of gases.
• Dalton’s law of partial pressures states that the total pressure (P T ) of a mixture of gases is the sum of the partial pressures of the individual gases (P A , P B , P C , etc).
• Stated mathematically, P T = P A + P B + P C + …
• A 10.0 L container of helium at 3.6 atm is separated from a 4.2 L container of nitrogen at 6.7 atm by a valve. What is the total pressure after the valve has been opened?
• First, solve for the partial pressure of each gas in the final volume using Boyle’s law (P i V i = P f V f ).
• The total pressure is the sum of the two partial pressures. Notice that total pressure (4.5 atm) is between the two initial pressures.
• The mole fraction (X) is the moles of a substance (n A )
  divided by the total moles of all substances in a mixture (n T ). The mole fraction is related to the partial pressure by the equation P A = X A P T .

Question 3

Two gas tanks are linked by a connecting tube with a valve. This time, one contains 6.5 L of oxygen at 5.4 atm of pressure. The other contains 9.0 L of argon at 3.7 atm of pressure. If the valve is opened, what is the final pressure of the two tanks combined?

Answer 3

4.4 atm

Question 4

Two gas tanks are linked by a connecting tube with a valve. One contains 12.0 L of oxygen at 4.0 atm of pressure. The other contains 6.0 L of argon at an unknown pressure. When the valve is opened, the final pressure of the two tanks combined is 3.8 atm. What was the original pressure of argon in the one tank?

Answer 4

3.3 atm

Question 5

Two gas tanks are linked by a connecting tube with a valve. One contains 10 L of helium at 6.7 atm of pressure. The other contains 4.2 L of nitrogen at 3.6 atm of pressure. If the valve is opened, what is the final pressure of the two tanks combined?

Answer 5

5.8 atm

Question 6

A tank of gas is found in the coldest part of the refrigerator (at “standard temperature,” 0°C = 273 K). It contains 4 moles of gas: 1 mole of oxygen and 3 moles of neon. The volume of the tank is 11.2 L. What is the partial pressure of oxygen in the tank?

Answer 6

2.0 atm

Question 7

There are two helium cylinders; cylinder 1 is bigger than cylinder 2. If each contains the same amount of helium gas, what can we say about the pressure of helium gas in the cylinders?

Answer 7

The pressure in cylinder 1 is less than in cylinder 2.

Question 8

A tank of gas at 25.0°C contains 2.0 moles of hydrogen and 4.0 moles of helium. The volume of the tank is 11.2 L. What is the partial pressure of helium in the tank? (R = 0.08206 L • atm / mol • K)

Answer 8

8.7 atm

Question 9

Two gas tanks are linked by a connecting tube with a valve. One contains 6.5 L of oxygen at 5.4 atm of pressure. The other is 9.0 L in volume and contains a vacuum (it is empty of any gas molecules). If the valve is opened, what is the final pressure of the two tanks combined?

Answer 9

2.3 atm

Question 10

What is Dalton’s law?

Answer 10

PTotal = P1 + P2 + P3 + …

Question 11

The Haber-Bosch process is used industrially to produce ammonia (NH3 ) from nitrogen and hydrogen through the reaction
N2(g) + 3H2(g) → 2NH3(g)
After running the process in a 612 L tank at 559°C for three hours, 242 moles of ammonia have been produced and 128 moles of H2 remain. If the initial total pressure of the system was 127.7 atm, what was the initial partial pressure of N2?

Answer 11

72.9 atm

Question 12

What does the mole fraction of a gas in a tank which contains a mixture of gases equal?

Answer 12

It is equal to the ratio of the number of moles of a particular gas to the total number of moles of gas in the tank.