How Does Altitude Affect the Properties of Helium in a Balloon?

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SUMMARY

The discussion focuses on the effects of altitude on the properties of helium in a balloon. As the balloon ascends, the external pressure decreases, leading to changes in the density and volume of the helium, while the number of moles remains constant at 207 moles. The mass of the helium decreases with lower temperature, but the internal pressure of the balloon remains constant throughout the ascent. The calculations confirm that the upward force exceeds the downward force, allowing the balloon to rise.

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Homework Statement


I have a balloon on the ground, where it is 20 degrees celsius, and it has a volume of 5L (it is filled with helium). The pressure at the ground is 1 atmosphere. The balloon itself (without helium) weighs 0.1 kg.

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

F_up = (m_air)*g = 58.96 N

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

So the balloon will go up.

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

The Attempt at a Solution


My questions are:

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

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