Students are studying how two substances react. the students mix substance 1 with substance 2 in a solution. later the students boil the solution, releasing substance 1 as a gas and leaving substance 2 as a solid. what type of change is described in the paragraph above? how do you know? this is a chemical change, because the two substances were mixed together. this is a chemical change, because the two substances were separated chemically by boiling. this is a physical change, because the two substances were separated physically by boiling. this is a chemical change, because a gas was released.