Question

Is atmospheric(Air) pressure higher or lower when boiling water WITH a lid on?
What Degrees would the air inside the pot(Steam) be with and without the lid?

Answer 1

this is a fairly easy concept to understand. The first thing you need to know is what causes pressure; In this case it is the air on top of the water that is causing the pressure on it(the water is being pushed by the air above it.



Now, if the air pushing down has more energy it is going to push down 'harder'. So in your case, you are putting a lid on the top, preventing the steam (which has a high kinetic energy) from escaping, and the pressure keeps on building up untill there is too much to handle. just like a balloon will pop if you heat it up too much. I think the steam will be just over 100 C without the lid and with the lid, there is nothing stopping it from going a bit higher because the lid is holding it down.