Three gases, nitrogen, helium, and krypton are confined in a 9.00 L vessel at a

Question

Three gases, nitrogen, helium, and krypton are confined in a 9.00 L vessel at a pressure of 7.00 atm. The vessel contains 5.00 moles of nitrogen, 2.00 moles of helium, and 2.00 moles of krypton. What is the partial pressure of helium?

1. Partial pressure of helium = ? atm

Now suppose that 8.00 moles of neon are added to the vessel without changing the volume or temperature. What is the partial pressure of helium now?

2. Partial pressure of helium after addition of neon = ? atm

Now suppose that an additional 5.00 moles of helium are added to the vessel, again without any change in the volume or the temperature. What is the partial pressure of helium now?


3. Partial pressure of helium after addition of 5.00 more moles of helium = ? atm

Explanation / Answer

Partial pressure is proportional to mole fraction. So, you have 9 moles of gas, and 2 of those are helium. So, the mole fraction of Helium is=2/ 9 = 0.22 Multiplying that by the total pressure gives the partial pressure of N2: 7 atm X 0.22 = 1.54atm Now, the mole fraction of Helium = 2/9+8 =2/17 =0.117 Under the conditions in the first problem, 1 mole of gas exerts a pressure of 7atm/11 mol = 0.636 atm/mol. So adding 8 mol Neon will increase the pressure by 5.08atm, making the total pressure =5.72 atm. the partial pressure of He is 0.117X 5.72 = 0.669 atm. Now, the mole fraction of Helium = 7/22= 0.318. Figure out the total pressure as before and multiply by the mole fraction Helium

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