Homework Help: Chemistry and gas law problems

1. Apr 16, 2012

janesmith

Hello. If somebody has time can you check my answers?

Q1: A gas occupies a 2.0L container at 25°C and 2.0atm. If the volume of the container is halved and the temperature remains constant, what is the new pressure?

P1V1 = P2V2

P2 = 2.00 atm x (2.00L / 1.00L) = 4.00 atm

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Q2: The volume of 50mL of an ideal gas at STP increases to 100mL. If the pressure remains constant, what is the new temp?

V1/T1 = V2/T2

T2 = (100mL / 50 mL) x 273K
T2 = 546K

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Q3: How many moles of Oxygen gas, O2, are present in a 3.5L container held at a pressure of 0.5atm and a temp of 77°C?

n = PV/RT

n = (0.5atm x 3.5L) / (0.082 L•atm/mol•K x 350K)
n = 50.225 mole O2

Thanks in advanced if you take the time to check these for me.

2. Apr 20, 2012

JameB

Your method is correct, I didn't check your math. You have a calculator for that!

Good luck!

3. Apr 21, 2012

Staff: Mentor

This MUST be wrong. At STP 1 mole of gas occupies 22.4 L. 0.5atm and 77°C is not STP, but it is also not that far - so 3.5 L should be just a fraction of a mole, not 50 moles.