Why does a sealed gas balloon expand when it is brought from ground level to the top of a mountain?

Answer 1

the air is less dense at altitude, therefore it exerts less pressure. the gas in a sealed balloon will exert the same pressure regardless of it's altitude, so, with less outside pressure to overcome, the balloon will expand.

Answer 2

The outside air pressure keeps the air molecules inside the balloon from expanding the balloon freely as far as it can go. Air molecules in the atmosphere are constantly colliding, and the collisions of outside air molecules with the surface of the balloon keep it from expanding further (countering the tendency of air molecules inside the balloon to push the balloon's rubber outward). As you go up a mountain, the air becomes thinner as the air pressure decreases; that is, there are fewer air molecules in a given volume of atmosphere. Thus, fewer outside air molecules are present to collide with the balloon's outer surface and the molecules inside have less resistance when they hit the inner surface of the balloon, forcing it outward and increasing the volume of the balloon.

As you can see, there is no increase of gas in the balloon, but the decrease in atmospheric pressure allows the existing gas molecules inside the balloon to overcome the outside pressure and expand its volume.

Answer 3

Helium balloons continue to rise as long as they are lighter than the surrounding air, as long as the balloon can keep its structural integrity, and as long as it doesn't leak. It is all about buoyancy.

Answer 4

As the ballon ascends the air pressure decreases and the balloon expands.