# Homework Help: Predicting the temperature of absolute zero experimentally

1. Apr 2, 2013

### PhizKid

1. The problem statement, all variables and given/known data
A metal ball with pressure gauge at room temperature and standard pressure is immersed into three different liquids each with different temperatures in succession (the three liquids are alcohol in dry ice, boiling water, and freezing water), and then is immersed into these liquids in different orders for each respective sequence. At the end of each sequence, the device is immersed into the alcohol and dry ice and the valve on the pressure gauge is opened until the pressure reads that of standard pressure, and then the valve is closed again before continuing on to the next sequence. What is the purpose of opening the valve in the alcohol with dry ice then closing it before immersing it into the other liquids?

2. Relevant equations
N/A

3. The attempt at a solution

I would think that you have to leave the device alone until it reaches standard temperature by itself before moving on to the next sequence. I don't understand why you have to do this at all. Doesn't make any sense to me.

2. Apr 2, 2013

### voko

Do you have "standard temperature" available in the setup?

3. Apr 2, 2013

### PhizKid

Yes, the room temperature is 25 degrees at 15 psi measured using the tool

4. Apr 2, 2013

### voko

I would think that the room temperature is too unstable, and that it takes too long to reach equilibrium by heat exchange with the room air.

5. Apr 2, 2013

### PhizKid

But by opening the valve inside the dry ice, it releases the pressure and after you close it, the pressure begins to drop below the the initial room pressure. So at the same room temperature, won't the device display a pressure lower than 15 psi because of the calibration made inside the dry ice which would produce an inconsistency?

6. Apr 2, 2013

### voko

The real question here is whether the system reaches thermal equilibrium when immersed into the dry ice. I would think it should for the step to make sense, because it is only then when one can deduce how much gas in inside.

7. Apr 2, 2013

### PhizKid

I believe it is assumed that thermal equilibrium in the system is achieved. Even so, why does this make sense to release the valve then re-close it in the dry ice?

8. Apr 2, 2013

### voko

The cooling bath made of alcohol and dry ice has a well defined temperature, below that of the freezing and boiling water. The more the difference is, the more accurate your results will be. It is much better than the room air for this reason.