What are 4 different forms of evidence for a chemical reaction?

Answer 1

Evidences For Chemical Change

Chemical changes produce new substances from starting substances, and distinguishing a chemical change from a physical change is based on detecting new substances in the system being observed. When two or more materials (reactants) are mixed, four easily observed indicators for new materials are:
1) formation of a gas from two liquids or a liquid and a solid.
2) formation of a solid (precipitate) from two liquids or a gas and a liquid.
3) unexpected color change. For example, mixing two colorless liquids and obtaining a color is an unexpected color change but mixing a blue liquid and yellow liquid and obtaining a green liquid is not an unexpected color change.
4) dissolving an insoluble solid (precipitate) in a solution. Note, the solution's solvent in this case will not dissolve the solid by itself.
Not all chemical reactions exhibit these changes in properties, and evidence for new substances must then be obtained from other observations. Instruments which extend our ability to make observations are often employed to detect such chemical changes.

Answer 2

synthesis, decomposition, single replacement, and double replacement. hope this helps you.