Use the ideal gas law to explain why a hot air balloon floats?

Question

thanks.

Answer 1

First use the ideal gas eq; solve for volume:

PV = nRT ---> V = nRT/P:

Now we will take 1 mole of gas at 1 atm and see what happens if we heat it:

For one mole at 1 atm, at 0C (273K):

V = 1 mole x 0.08206Latm/moleK x 273K/1atm = 22.4 liters which you were probably already aware; one mole of gas at STP is 22.4 L.

Now if we heat the same gas to 100C (373K) and solve for the new volume.

V = 1 mole x 0.08206Latm/molK x 373/1atm = 30.6 liters.

Heating the gas and leaving all other factors the same resulted in an increase in volume. If the volume got bigger and the pressure and number of moles didn't change, then the gas had to get less dense to fill the larger space. This is what makes the hot air balloon float in the air.

Answer 2

well, a regular balloon, when filled up with someones breath, is a relatively low temperature compared to a hot air balloon. Hot air balloons also operate at higher altitudes (and temperatures), where the air is thinner and cooler. As you know, heat rises, and pushes on the top of the balloon's fabric, pulling the basket up.