Thermal Equilibrium of a Cold Balloon in a Warm Room

What happens when a cold balloon filled with air is placed in a warm room?

A) it rises to the ceiling

B) it stops expanding

C) it sinks to the floor

D) it starts to contract

Answer

The balloon is NOT in thermal equilibrium with the air of the room until it stops expanding and reaches the same temperature as the air in the room.

When a balloon filled with cold air is placed in a warm room, the air inside the balloon starts to warm up. As the air molecules gain thermal energy, they move faster and exert more pressure on the walls of the balloon. This increased pressure causes the balloon to expand.

However, the balloon is not in thermal equilibrium with the air in the room until the air inside the balloon reaches the same temperature as the air in the room. At this point, the balloon stops expanding and maintains a constant size.

Thermal equilibrium is reached when there is no net transfer of heat between the balloon and the surrounding air. In other words, the rate of heat transfer into the balloon is equal to the rate of heat transfer out of the balloon. This occurs when the temperatures of the balloon and the surrounding air are equal.