Does a balloon's temperature increase when a balloon is popped?

[Elizabeth Lil]

Homework Statement

We blew up a balloon, attached a data logger inside the balloon. We then popped it and checked if the temperature increased or decreased. Most of the time, the temperature increased (from around 29 degrees Celsius to 29.2 degrees Celsius).

Why is this so?

Homework Equations

Ideal Gas Law: Pv= nRT (where n and R are constants)

The Attempt at a Solution

My group is divided. One of us thinks that the balloon's temperature should have decreased, as the pressure decreases (following the Ideal Gas Law up there). But another of us thinks that it should have increased, because the volume increased more than the pressure did.

 

[Simon Bridge]

Welcome to PF.
What is the thermodynamic process you'd expect to be dominant when the balloon was popped?

What was the mean and standard deviation of the changes over many experiments?
Did you pop the balloon by inflating it until it burst or just pricking it with a pin?

 

[Elizabeth Lil]

We popped the balloon with a pin.

Our results show that the temperature of the air in the balloon either remained the same or increased by about 0.2-0.3 oC, but we're not sure if this is theoretically correct or simply due to human error. The mean over all our experiments should be around an increase of 0.06 oC or so.

If our results are correct, then I suppose the increase in volume took precedence over the decrease in pressure. But is that likely to happen?

 

[Simon Bridge]

You will get experimental variation due to lots of things - including variations in the composition of the balloons. It is just not the same each time. You'd expect so many random variations to produce a normal distribution in your results ... which is why mean and standard deviation are important. If "no change" is within 2sd of the mean change then your results are consistent with no change in temperature. (If there were any change, you failed to measure it.)

BTW: did you measure the pressure inside the balloon?

If our results are correct, then I suppose the increase in volume took precedence over the decrease in pressure. But is that likely to happen?

Well that is the question isn't it? So think of the different thermodynamic processes and ask which one you'd expect to be dominant. Should have done this before the experiment... it is seldom meaningful to confirm a theory after the fact.

Note: experimental results are always "correct". They are what you measured.

 

[ehild]

Do not forget the elastic wall of the balloon. While the gas extends through the hole into the external atmosphere and does work against the external pressure, the walls move inward, pressing the gas out. This is work done on the gas, warming it up, while the extension of the gas results in cooling down.

ehild