The amount of heat absorbed when 1 kg of a substance changes from solid to liquid at its melting point is equal to its latent heat of fusion.

Here's why:

* Latent Heat of Fusion: This is the amount of energy required to change a substance from a solid to a liquid at its melting point, without a change in temperature.

* Melting Point: The temperature at which a substance transitions from a solid to a liquid.

Important Note: The heat absorbed during the phase change is used to break the bonds holding the solid structure together, not to increase the temperature.