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MCAT Question A Day - 4/4/14 - Answer!

Which of the following will not change the total pressure in a closed vessel containing N2 gas? (Assume ideal gas behavior.)

I.  Increasing the temperature
II.  Replacing half the N2 molecules with gaseous helium atoms
III.  Adding an equal amount of gaseous hydrogen

A.  I only
B.  II only
C.  III only
D.  I and II only

The correct answer is (B). The pressure exerted by a gas depends on the total number of molecules, not on its molecular weight or the number of atoms per molecule. Changes in T, however, will affect the pressure.

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