Question

How are vapour pressure and boiling point inversely related?

Answer 1

On top of a mountain where air pressure is low the boiling point is low and it takes longer for food to cook.

Answer 2

The premise that vapour pressure and boiling point are inversely related is incorrect.

Explanation:

Most liquids express a vapour pressure at a given temperature. This may be related logarithmically, for which see the Clapeyron equation for phase equilibria.

When the vapour pressure expressed by the liquid is equal to the ambient pressure, and bubbles of vapour form directly in the liquid, the liquid is said to be boiling.... The normal boiling point is specified as the temperature when the vapour pressure of the liquid is ONE ATMOSPHERE.....

And thus if we reduce the ambient pressure, we may REDUCE the boiling point of the liquid....in that we may heat it to a LOWER temperature to reach the boiling point. And this is the principle of `"vacuum distillation"`, where an otherwise involatile liquid, is subjected to high (or reduced) vacuum, such that its vapour pressure matches the ambient pressure, and the liquid distils under vacuum...to give a pure distillate....

On the other hand, when we cook in a pressure cooker, we RAISE the ambient pressure, the boiling point of the liquid (usually water) is RAISED above `100` `""^@C`. I had a colleague who cooked curries with beautiful, tender meat in an hour in his pressure cooker, rather than simmering for 5-6 hours or longer.