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?