Question

You have a balloon that contains 1 kg of helium that occupies a volume of 4 m Sometime later, the balloon still holds 1 kg of helium, but it now occupies a volume of 2m'. Your friend suggests that the helium can be considered an isolated system in this case. Can they be correct?

Answer 1

Yes! They can be correct

Step-by-step explanation:

An isolated system is a system where its total energy and mass stay constant.

In this case, even though the volume changed, the mass remains constant (m = 1 kg), so there is no mass exchange, and we must think that the globe is completely closed.

Now, we don't know exactly what happens with energy, but I can give you an example where the total energy of the globe remains constant.

Imagine that the balloon of volume
`V_1` is at a certain height
`h_1`, under some pressure,
`P_1`. If you lower the balloon to a height
`h_2`, the pressure increases, and from the Boyle's law,

`P_1 V_1 = P_2 V_2`,

`V_2 = V_1 (P_1)/(P_2)`, where
`P_2 > P_1`,

`V_2 < V_1`, just like the case you state, and there was no exchange of mass or energy related to the inner gas of the balloon, so yes, They can be correct.