Is heat being added or taken away when water boils?

2 Answers
Jul 23, 2018

See below


Heat is being added in a way that does not result in a temperature change in the water, but that heat energy is used to increase the Potential energy of water by increasing the amount of space between each of the water molecules.

Jul 24, 2018

Well, when the water boils it undergoes a phase change...


And so....

#underbrace(H_2O(l)+Delta_"vaporization" rarrH_2O(g))_("both water and steam are "100""^@C)#

Now clearly, energy has to be added to water to get it to the boiling point. But once at the boiling point, MORE energy has to be expended to effect the phase change between water as a liquid, and water as a gas, i.e. steam.

For water, #DeltaH_"vaporization"^@=+40.7*kJ*mol^-1#, and thus heat is ADDED....