# Chemistry help needed......

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I'm posting this in case anyone one here can help a student I'm working with (obviously I'm NOT working with her in chemistry:D) She's absolutely stuck on these two homework problems and can't get ahold of her teacher.

1. The total mass that can be lifted by a baloon is equal to the difference between the mass of gas in the balloon and the mass of air displaced by the balloon.

*How much mass could be lifted by the balloon?

**How much mass could the same balloon lift it it was filled with helium at the same pressure and temperature?

2. Use the barometric formula P=P0e=-Mgh/RT to estimate the height to which the balloon with a payload of 1000kg can rise when filled with hydrogen. (The balloon will rise until the density equals that of the surrounding air.) Assume that the temperature fo the air does not change with altitude. Use the average molar mass M (in kg) for air based on 80% N2, 20% O2, and use 9.81 m s-2 (Hint: first reassure yourself that the mass of displaced air inside the balloon is proportional to the atmospheric pressure)

So, anyone up for the challenge this late at night?

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Thought I give it another try. Just got an e-mail from my student and she heads to class in another hour and a half. Any suggestions?

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1. The total mass that can be lifted by a baloon is equal to the difference between the mass of gas in the balloon and the mass of air displaced by the balloon.

*How much mass could be lifted by the balloon?

**How much mass could the same balloon lift it it was filled with helium at the same pressure and temperature?

The problem is incomplete. The first question can only be answered if the student knows what gas is inside the balloon, and what the radius or volume of the balloon is (or if the two masses are explicitly given)

The balloon displaces the amount of air that corresponds to its volume, so you need to use the volume to find out how much air is displaced.

(The above statement is correct only if the mass that is lifted does not take up any room (point mass) and the hull of the balloon is massless.)

The second part can be answered if the original gas in the balloon is replaced with He.

I have to run to work and don't have time to look at the second problem now.

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