You collect 6.36 moles of hydrogen gas from your lab experiment involving the decomposition of water by electrolysis. The pressure inside your rigid collection vessel is at 1.00 atm. Another lab group adds their collected gas to yours, giving it an additional 1.28 moles. What is the new pressure inside the container?

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The number of moles of a gas is directly proportional to the pressure of the gas at constant temperature and volume.

This comes from the ideal gas law:

PV=nRT or PV/nT = R, a constant

We can assume constant volume because the container is rigid, and there's no indication that...

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The number of moles of a gas is directly proportional to the pressure of the gas at constant temperature and volume.

This comes from the ideal gas law:

PV=nRT or PV/nT = R, a constant

We can assume constant volume because the container is rigid, and there's no indication that the temperature changed. 

When V and T are unchanged they can be left out of the equation so P/n equals a constant. When pressure and number of moles change, P1/n1 = P2/n2.

We can rearrange this to solve for the new pressure: P2 = (P1)(n2)/n1

P1 = 1.00 atm

n1 = 6.36 moles

n2 = 6.36 moles + 1.28 moles = 7.64 moles

P2 = (1.00 atm)(7.64 mol)/(6.36 mol) = 1.20 atm

This answer is consistent with what we expect, a higher pressure because the number of moles of gas increased.

 

 

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