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A rigid closed container of volume 8.21 L holds 4 mol N2 and 6 mol O2 at 400 K (R = 0.0821 L·atm/(mol·K)). Which of the following statements are correct?

1. Partial pressure of O2 is 24 atm.
2. Partial pressure of N2 is 16 atm if 2 mol of He is added.
3. Partial pressure of O2 is 24 atm if 2 mol of N2 is removed from the container.
4. Total pressure of the container increases when 2 mol of He is added.

Correct answer: Partial pressure of O2 is 24 atm.

Solution

Total pressure = (10 mol * 0.0821 * 400)/8.21 = 40 atm. All four options are individually correct: (A) P(O2)=24 atm initially; (B) adding 2 mol He → 12 total mol, P=48 atm, P(N2)=(4/12)*48=16 atm; (C) removing 2 mol N2 → 8 mol, P=32 atm, P(O2)=(6/8)*32=24 atm; (D) adding He always increases total pressure.

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