A balloon filled with helium has a volume of 43.4 L at 305 K. What volume will the balloon occupy at 273 K?

To solve this, you need to use a relationship for gases known as Charles' Law. Charles' Law says that at a constant pressure, volume and temperature have a direct proportionality relationship. The equation accompanying this is:

(V1) / (T1) = (V2) / (T2)

We have 3 known values so we can solve for the fourth:

V1 = 43.4 L

T1 = 305 K

T2 = 273 K

V2 = Unknown

Plugging into our equation:

(43.4 L) / (305 K) = (V2) / (273 K)

V2 = (43.4 L/305K) * (273 K)

V2 = 38.8 L = Volume the balloon occupies at 273 K

This makes sense, as a hotter gas will have more average kinetic energy, and would take up a large volume. When the volume was calculated at a lower temperature, the calculated volume decreased as expected.