The heat required to change a unit mass of a solid to a liquid at the melting point is called the

I believe it is called the latent heat. 

Have a goodnight! 

Ifound this on google “these two compounds have a different ionic structure. caesium ion is larger in size when compared to the sodium ion. the charge gets more area to spread out evenly. so caesium chloride has a lower melting point than sodium chloride.” i hope this you for what your looking for