As we heat an hot air balloon, the gas doesn't expand adiabatically.... Or does it?

[September24]

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I was looking why a hot air balloon only rises to a certain height as we heat it up. I came to an answer tha days "as we heat the gas, the gas expands adiabatically and thus cools. Since cooler air is more dense, the balloon stops rising".

I thought that since we are literally adding heat, heat would be added (to expand the molecules) and the process would not be adiabatic.

As we temperature of the balloon goes up, energy would go up right? If the gas was expanding adiabatically,

E=0-PV(work done by gas)

If it is expanding, it would be doing work and cooling.

But how is it cooling...as we are heating it?

 

[ipmed]

As you heat a gas, it expands and has a larger volume, so it exerts a larger buoyant force that causes it to rise. BTW the buoyant force is exerted by the air surrounding the balloon. correct me, if iam wrong