I put water in a thermos and shut it tight. 2 says later I open it and there’s a small release of gas. Why?
In: 1
Could be any number of reasons. Temperature changes result in a change of pressure in the gas already in it. Or dissolved gas in the water comes out and since water doesn’t really compress, this changes the pressure of the gas instead. When you open it up, that increase in pressure results in air gushing out.
The water warmed and expanded slightly over the two days the thermos was sealed, pressurizing the container. When you broke the seal, the pressure was released. And, some air was pushed out.
You put cold liquid in the thermos, it heats up. The little amount of air in the thermos also heats up, so it’s pressure rises. Now the pressure inside the thermos is higher than ambient pressure. As you open the lid, higher pressure air trapped inside rushes out.
You put hot liquid in the thermos, it cools down. The little amount of air in the thermos also cools down, so it’s pressure drops. Now the pressure inside the thermos is lower than ambient pressure. As you open the lid, higher pressure ambient air rushes in.
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