# Stuck on ideal gas law question

1. Jul 10, 2008

### nicksim117

1. The problem statement, all variables and given/known data
On a warm day 90F, the air in aballon occupies a volume of .25m3 and exerts a pressure of 20 lb/in2. If the baloon is cooled to 30F in a refrigerator, the pressure drops to 14.2lb/in2. What is the volume of the balloon

2. Relevant equations
P1xV1/T1=P2xV2/T2-----((P1xV1)/T1)xT2/P2
T1=305.2K
T2=271.88K

3. The attempt at a solution
.31m3 is the answer i keep getting How is this possible when this volume is larger than the original.

2. Jul 10, 2008

### Tom Mattson

Staff Emeritus
You've got two competing effects here. First, there's a temperature drop, which tends to make the balloon shrink. But you've also got a pressure drop, which tends to make it expand. It just so happens here that the effect of the pressure drop dominates the effect of the temperature drop, hence you have a larger balloon.

3. Jul 10, 2008

### nicksim117

But the pressure drop is inside the balloon.

4. Jul 10, 2008

### nicksim117

There is no way you are going to have a larger balloon when you cool it down in a freezer.

5. Jul 10, 2008

### HallsofIvy

What values did you use for T1 and T2? In the ideal gas law, termperatures must be given in degrees Kelvin.

6. Jul 10, 2008

### nicksim117

I listed them in the problem T1 305.2 T2-271.88

7. Jul 10, 2008

### Tom Mattson

Staff Emeritus
Yes that's true. And how that pressure drop is achieved, I do not know as the problem doesn't say. All I know is that under the temperature and pressure drops given in the problem statement, you do in fact get a larger volume.

It could be that the data given in the problem is unrealistic, but your calculation is nonetheless correct.

8. Jul 10, 2008

### dynamicsolo

I suspect this is yet another case of someone making up a problem without checking to see if the given information makes sense in terms of a natural process. I don't really believe that the pressure in the balloon would drop to that value by chilling it in the fridge that way. However, the answer of 0.314 m^3 is what you get from the ideal gas law using that information. (Yeah, right: I wanna see how they got a balloon with a diameter over 60 cm. into the refrigerator to start with... Maybe it's a "walk-in"...).

The point is that, for the purposes of this problem [grinds teeth], the balloon would have to have expanded and cooled from its initial state in order to reach that final state. You did the problem right -- it's not your fault it makes little sense...

9. Jul 10, 2008