### When a balloon is dunked in liquid nitrogen, it shrivels up.

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Teachable Topics:

• Ideal Gases
• Volume and Temperature relationship

Theory:

When we blow up a balloon, we are filling it up with gas from our lungs, at normal room temperature and pressure, it stays in a nice round shape. When it is dunked into the liquid nitrogen, it shrivels up and shrinks. Why is this? It is because of the relationship between pressure, volume and temperature, which can be described using the ideal gas law. The ideal gas law is stated as P*V = n*R*T, where P = pressure, V = volume, n = number of moles, R = gas constant (8.314 J/mol*K) and T = temperature. In this situation, pressure, moles, and the gas constant stay the same throughout the process. That means that

Vbefore / Tbefore= (n * R) / P = Vafter / Tafter
Vbefore / Tbefore= Vafter / Tafter

So that means that any change in temperature is going to have an effect on the volume, since temperature and volume are directly proportional.

If we were to decrease the temperature of the balloon from room temperature ( 25o C or ~298K) to the boiling point of liquid nitrogen (-196oC or ~ 77K) our Vafter would be

Vbefore / Tbefore= Vafter / Tafter

Vbefore / (298 K)= Vafter / (77 K)

0.2584 Vbefore = Vafter

So the end volume is about a quarter of the original volume, just like the end temperature is about a quarter of the original temperature. Thats why the balloon shrinks when it is dunked in the liquid nitrogen and why it expands again as it warms up.

Apparatus:

• Liquid Nitrogen
• Safety gloves
• Tongs
• Goggles
• Balloons

Procedure:

1. Blow up a balloon until it is just big enough to fit in the container of liquid nitrogen.
2. Pick up the balloon with tongs and lower it into the liquid nitrogen.
3. Observe how the balloon shrinks.
4. Once it is as shrivelled up as it will get, raise the balloon out of the liquid nitrogen.
5. Hold it in the air or place it on a warm surface and observe how it appears to inflate again.

Safety:

Be very careful when using liquid nitrogen, wear safety goggles and cryogenic gloves.