Question

1) why melting point is a constant temperature?

2) why boiling point is a constant temperature?

Answer 1

1) The temperature change is caused by sensible heat.The substance is in the solid region and is absorbing heat at constant pressure. When the temperature reaches the melting point at the corresponding pressure, the substance absorbs latent heat of fusion.

2)Temperature and Boiling. When boiling occurs, the more energetic molecules change to a gas, spread out, and form bubbles. In addition, gas molecules leaving the liquid take away heat energy. Therefore the temperature of the liquid remains constant during boiling.