Question

Which has higher air pressure when boiling water, lid or no lid?

Answer 1

This question is not very well phrased.

'Atmospheric' pressure is normally taken to mean the ambient pressure surrounding the 'experiment'. It is clear that this does not change when the lid is put on.

HOWEVER - what I THINK the question means is whether the pressure above the boiling fluid changes.

If you think about it - the steam has to 'lift the lid' to escape - so the pressure must increase over when there is no lid.

You know the temperature that water boils in atmospheric pressure - but you cannot answer the second part unless you know the ACTUAL pressure inside the pot with the lid on

Answer 2

has anyone ever made a decent cup of tea on the summit of Mount Everest?

if not, why not?

Answer 3

you can make a statement about the RELATIVE value of the temperature - but unless you know the actual pressure you cannot put a number "degrees" on the change of temperature

Answer 4

@MrNood so without the lid on the air pressure is greater? This question is about how boiling process is a cooling process.