Can all solids be changed to liquids?
No; there are many solids, such as wood, coal, paper, and leather, that cannot be changed to liquids.
How can a liquid be changed to a solid?
By taking heat away from the liquid, it may be changed to a solid.
Why is a solid melted by heat?
Because heat forces the particles of the solid apart, until it is changed to a liquid.
Latent Heat.
Why does warm iron feel warm to the hand?
Because it gives off some of its heat to the hand.