Question

When a liquid boils, its temperature remains the same, so where does the heat go?

Answer 1

  Temperature is an average of the kinetic energy in a system. If a pot of water is at 90 °C, not every molecule of water has the same level of energy. Some will have an equivalent temperature of 95 °C while others will have an equivalent temperature of only 85 °C. 

Even before boiling occurs, steam starts to form. The steam is from molecules of water that already reached a temperature of 100 °C even though the average energy is below that level. When boiling has been reached, the molecules that are over 100 °C change from the liquid phase to the gas phase and leave the system. This continues so that the molecules at or just under 100 °C stay a liquid while those above leave. Eventually all the water will reach 100 °C and all the water will turn to a gas and leave the pot.