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January 26, 2015

January 26, 2015

Posted by **paro** on Monday, April 5, 2010 at 1:23pm.

What is the final pressure of the gas?

- physics -
**drwls**, Monday, April 5, 2010 at 3:42pmIn isothermal expansions, the product

P*V = a constant. Therefore

P2/P1 = V1/V2 = 50/200 = 1/4

Since you were not told the initial pressure P1, you will have to use the perfect gas law and the information given.

0.11 moles at STP (1 atm and 273K) occupies 0.11*22.4 = 2.46 liters. At 10C (283K) it would occupy 2.55 liters. Since the initial volume is only 50 cm^3 = 0.05 l, the initial pressure must be

P1 = 2.55/0.05 = 51 atm.

The final pressure is 1/4 of that.

You could also have used P = nRT/V to get the initial pressure. Personally I find it easier to remember that 1 mole is 22.4 liters at STP. There are too many values of R, with different units, to try to remember.

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