Science Buddies: "Ask an Expert"

My question is does water boil faster with a lid on or off and what is the science behind it? JO

Welcome to the Ask the Expert forum. I maybe missing something, but I read your post as a statement (of your scientific question). What are you trying to Ask us (the Experts)?

This is a great example of thermodynamic processes. For your system of water in a pot, heat is added to do work (i.e. boil water) in 2 ways. 1) with the lid off is an Isobaric process and occures at a constant pressure (that of the outside air). 2) with the lid on is an Isometric process and occures at a constant volume. I invite you to search online for deeper explanations for these terms to really get all the science behind them.

The key thing to remember is that Temperature (T) is proportional to Pressure (P) and inversely proportional to Volume (V). At constant V (lid on) as heat is added there is nowhere for water vapor to go and P increases causing T to rise with it. With lid off, water vapor (steam) is allowed to escape and as V increases, T decreases causing the system to heat up slower than the Isometric process. So this is more a discussion of the Ideal Gas Law, but the principle holds true at the relatively low temp and pressure ranges involved. For more reading on this I attach the following website: http://hyperphysics.phy-astr.gsu.edu/hb ... degas.html

Hope this helps. Enjoy.

It's also helpful to remember that the time it takes a pot to boil is directly related to the amount of optical observation.