First law of thermodynamics: Boiling off water in a kettle.
The heat is supplied : Q is positive
Work done on the gas: W is negative
change in U = Q + W , is positive. The increase in U is not due to increase KE but due to increase in PE . Even though the temperature remain at boiling point , however the water is not ideal gas so there is increase in PE as the molecules have inter atomic forces. Work done to separate the molecules increase the PE but KE remain constant hence temperature remain at boiling point,
