Diving Physics Puzzle

[beachegirl]

Got this question from an anatomy class and it has puzzled me... possibly a bad question?
So here is a brain teaser for those willing to take the challenge. Let me know what you think.

If you had a balloon in which ppO2 was 150mm Hg and ppCO2 was 50mm Hg and you deflated it to half the volume, what is the new ppO2 and ppCO2? What would happen to the ppO2 and ppCO2 if you filled the balloon back up to volume with air?

 

[Tigerman]

First thought, the volume would decrease the pp would stay unchanged.. untill you filled it back up with air..

That answer however for various reasons are wrong

 

[Thalassamania]

Neither ppO2 changes with deflation. Using the simplifying assumption that there is no CO2 in air and that the ppO2 of air is 160mm Hg, after adding air the ppCO2 will be 25mm Hg and the ppO2 will be 155mm Hg. Of course this also assume the pressure inside the balloon is exactly the same at half and full inflation.

 

[Tigerman]

Neither ppO2 changes with deflation. Using the simplifying assumption that there is no CO2 in air and that the ppO2 of air is 160mm Hg, after adding air the ppCO2 will be 25mm Hg and the ppO2 will be 155mm Hg. Of course this also assume the pressure inside the balloon is exactly the same at half and full inflation.

But ballons are elastic, so it wont be?

 

[ItsBruce]

The first part of the puzzle is a trick. Pressure is inversely proportional to volume in a closed system. Deflating the balloon means you are not dealing with a closed system. Therefore, the partial pressures do not change.

 

[Kaltim Diver]

Depends on whether you mean half deflate the balloon or compress the balloon somehow to half it's volume. As others say, balloons are elastic and pressure/partial pressure remains constant.

 

[fppf]

Actually, pressure inside a balloon will INCREASE as you deflate it. This is because the elastic is non linear and gets thicker and stronger as the balloon gets smaller.

 

[dumpsterDiver]

Actually, pressure inside a balloon will INCREASE as you deflate it. This is because the elastic is non linear and gets thicker and stronger as the balloon gets smaller.

I did not know that.

 

[fppf]

Yeah, cool way to try it, blow up one balloon all the way.
Then blow up a second one only 1/4 full. Connect the two balloons together with a piece of tubing and watch what happens. General logic says the big one will deflate and the small one will inflate. But what really happens is the small one will deflate the rest of the way.

 

[DevonDiver]

Fascinating....must try that.