# Melting point vs pressure

In my physics-class, I was told that,

"The melting point of the same substance changes under different pressure. But it can change in two different manner"

There are 2 different ways it can change:

$$(1)$$ For higher pressure , the melting point will be lower (Like water)
$$(2)$$ For higher pressure , the melting point will be higher.

Also ,

$$(1)$$ This case happens for those substances which decrease in Volume when changing from a solid to a liquid.
$$(2)$$ This case happens for those substances which increase in Volume when changing from a solid to a liquid.

I have two questions

$$(a)$$ Can someone give me some more examples of of substances for case $$(1)$$ and case $$(2)$$ . [I couldn't find any except 'water' that was told in my physics class]
$$(b)$$ Why does melting point vs pressure depend on Volume change Like this ?

• There are a variety of elements with denser liquids at the melting point. These include Si, Ge, Sb, Bi, and others. There are then a number of non-elemental materials as well. Commented Nov 9, 2020 at 16:39
• Are you familiar with the concept that, for a phase change of a pure substance, the change in Gibbs free energy is equal to zero? If so, are you familiar with the Clapeyron equation for a phase change? Commented Nov 9, 2020 at 17:02