Question

One summer morning, after drinking a soda, you tighten the cap back on its empty 20 ounce plastic bottle and leave it in your car. Returning to your car later that day, you find that the bottle has somewhat swelled up, looking like it is about to burst.

In terms of heat and thermodynamics, explain what has happened to this bottle.

Answer 1

According to ideal gas law, the pressure of the gas is proportional to its temperature. This is because at a higher temperature, the gas molecules have higher kinetic energy and hence they bang against the wall of the closed container harder.

When you the empty and closed soda bottle in your car in the summer, the temperature of the gas molecules inside the bottle increases because of the heat that's being supplied to the gas inside the bottle from the surroundings. Since the volume remains constant (because the bottle is capped), the pressure of the gas inside the bottle increases. And that's why the bottle appears to be swelled up after some time.