State if a chemical change has occurred. Give a reason for answer. A student mixes 2 unknown solutions together & notices a cloudiness forming.Also...

1st: A typical high school expt would be to mix two salt
solutions. The cloudiness is a PRECIPITATE (a new compound) so this is a chemical
change.

2nd: The iodine has SUBLIMED, it has turned from
solid into a gas without being liquid first. If you cool the iodine gas it will
RESUBLIME back into solid iodine. This is a PHYSICAL change where no new substance is
formed.

3rd: The nitric acid is reacting with calcium
carbonate to make calcium nitrate, carbon dioxide, and water. New substances are formed
- a chemical change.

4th: You would need to know what is
being mixed here. It is possible for heat to be made if a chemical or  physical change
has happened.