AP Chem
posted by Anna on .
Can someone please check these problems?
34. You fill a balloon with helium gas to a volume of 2.68 L at 23 degrees C and 789 mmHg. Now you release the balloon. What would be the volume of helium if its pressure changes to 632 mmHg but the temperature is unchanged?
3.35 L
38. If 456 dm^3 of krypton at 101 kPa and 21 degrees C is compressed into a 27.0dm^3 tank at the same temperature, what is the pressure of krypton in the tank?
16.8 atm
42. An experiment called for 4.83 L of sulfur dioxide at 0 degrees C and 1.00 atm. What would be the volume of this gas at 25 degrees C and 1.00 atm?
5.27 L
46. Pantothenic acid is a B vitamin. Using the Dumas method, you find that a sample weighing 71.6 mg gives 3.84 mL of nitrogen gas at 23 degrees C and 785 mmHg. What is the volume of nitrogen at STP?
3.65 mL
102. A steel bottle containes 12.0 L of a gas at 11.0 atm and 20 degrees C. What is the volume of a gas at STP?
123. L
Thanks =]

CorrecT!

All look ok except 38 and 46.
The answer on 38 is correct; I just wondered why you changed it to atmospheres since the problem didn't ask for it. For 46 I obtained 3.658 which I would round to 3.66 mL. 
I thought that you always had to use atm in the equations.

No, using atmospheres is necessary only in PV = nRT and then only when V is in Liters and R = 0.08206 (units are L*atm/mol*K). You may use P in kPa in that formula if you use R as 8.3145 J/mol*K.
When using P1V1/T1 = P2V2/T2 or one of the variations of that (P1V1 = P2V2 etc), P and V can be in ANY unit you choose as long as you keep the units consistent. That is, if P1 is in atm than P2 must be in atm. If P1 is in kPa or mm Hg, then P2 must be in kPa or mm Hg. The same holds true for volume; it need not be in liters but any unit of your choosing but you must be consistent. That is NOT true for T. T1 and T2 must be in Kelvin. 
How did you get #34?