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Elements, Compounds and Mixtures

What happens to the Temperature of a Solid
as it Melts to become a Liquid?

The graph below shows how the temperature changes with time
as a substance is heated at a constant rate. There are obvious
horizontal flat sections of the graph at the melting and boiling point.

Graph of Temperature against Time for a Substance

Below the melting point the substance is a solid.
the melting point the substance is a liquid.

At the melting point, although the substance is still being heated,
there is a time when the temperature does not change and the
graph is horizontal. During this time, all the extra heat which is
being added goes to overcome the force of attraction (the bonds)
between the particles of the solid as it turns into a liquid.
The process of melting requires extra energy - it is endothermic.

The temperature of a solid can never be raised above
its melting point at atmospheric pressure. When all
of the solid has melted, then the temperature of the
liquid will start to rise (continued on the next page).

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