Question

How do laws of conservation apply to changes of state?

Answer 1

In the question above it is not mentioned which law of conservation is the questioner talking about so we will consider the law of conservation of matter.
Law of conservation of matter states that matter can neither be created nor be destroyed.

Complete answer:
Law of Conservation of matter, It states that in the transfer of matter any given system that is closed to the transfer of matter, the amount of matter in the system stays constant. In other words we can say that the amount of matter contained in a substance is conserved.

When Ice is heated up one molecule of water having 3 atoms will remain the same even after the ice gets converted to water after consuming heat energy. No change in molecular mass or the number of atoms of the ice remain the same. Now, this water will consume more heat and as the water starts boiling the water gets converted to vapor at 1000C, the molecule of water remains the same even in the vapor form.

Note: There are other laws of Conservation, which are law of conservation of mass and law of conservation of energy. Law of conservation of mass is seen in Chemistry where a molecule breaks down into further atoms and sub atoms, the mass of the actual molecule will remain the same. Law of conservation of energy is seen when electricity is applied to a bulb it glows which means that electrical energy is converted to heat and light energy; no energy is created but converted from one form to another.