How would you use the kinetic theory to explain why a helium filled balloon "shrinks" when it is taken from a warm room to the outside on a cold day?

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Answer 1 · 2017-06-06T07:09:55

From kinetic theory, the pressure can be interpreted as, 2/3 the kinetic energy of molecules per unit volume.

$p = \frac{2 N E}{3} V$ $p = (2NE)/3V$

Also, from kinetic interpretation of temperature, the ideal gas molecules have their energy proportional to the absolute temperature.

Thus, $E = \frac{3 k T}{2}$ $E = (3kT)/2$

Combining the two relations,

$p V$ $pV$ is proportional to $T$ $T$ .

Then for a decrease in temperature $T$ $T$ , then $V$ $V$ and $p$ $p$ decrease.

This explains why the balloon shrinks when the temperature decreases.