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?

Question

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

Answer 1

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.