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Two identical flasks of equal volume are connected by a thin tube of negligible volume and sealed with a stopcock. One flask is kept at 250 K and the other at 750 K. After evacuating both flasks, 20 moles of an ideal gas are introduced into the system and the stopcock is opened. At equilibrium, what is the ratio of moles in the 250 K flask to the 750 K flask?

1. 1: 1
2. 2: 1
3. 3: 1
4. 4: 1

Correct answer: 3: 1

Solution

At equilibrium, pressure is the same in both flasks (P) and the volume of each flask is V. By PV=nRT: n1 = PV/(R*T1) and n2 = PV/(R*T2). So n1/n2 = T2/T1 = 750/250 = 3. Since n1+n2=20: n1=15, n2=5. The ratio is 3:1 (cold flask: hot flask).

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