# Homework Help: Ideal gasses and the law

1. Feb 6, 2008

### Niles

1. The problem statement, all variables and given/known data
I have a ballon on the ground, where it is 20 degrees celcius, and it has a volume of 5L (it is filled with helium). The pressure at the ground is 1 atmosphere. The ballon itself (without helium) weighs 0.1 kg.

I find the force that makes the ballon go up to be:

F_up = (m_air)*g = 58.96 N

F_down = (m_Helium + m_ballon) * g = 9.13 N

So the ballon will go up.

I can also find the number of Helium-moles from n = m/M, and I find that n = 207 moles.

3. The attempt at a solution
My questions are:

As the ballon goes up, the pressure goes down and so does the temperature. I want to know, which parametres are affected by this?

The density of the helium? Yes, because density is written as "rho" = M*p/(R*T), so this changes.

The volume of the helium? yes, this changes as well.

The number of helium-moles? No, this is constant too.

The mass of the helium? Yes, this gets smaller when the temperature goes down since "rho" = m/V.

The pressure inside the balloon? No, this stays the same.

Can you guys please confirm this?

Last edited: Feb 6, 2008
2. Feb 6, 2008

### Niles

- the pressure of the balloon is constant also, right?