What are four possible clues that a a chemical change has taken place?

Question

Wyatt Adkins · Accepted Answer

Difficult question, and of course the indicators I advance may be equivocal.

#i.# #"Change in colour"#, fairly unequivocal. A colour change is usually unambiguous evidence of chemical change. #ii.# #"Formation of a new substance"#, fairly unequivocal. Of course, how do you interrogate the formation of a new substance? This is especially true in organic chemistry, where products and reactants are (usually) colourless. #iii.# #"Change in enthalpy"#, this change is equivocal, as enthalpy change can also occur on phase change. #iv.# #"A change in characterizing chemical/physical properties"# #"occurs"#; i.e. change in melting point, boiling point, solubilities, chromatographic behaviour with respect to product and reactant. This change is fairly unequivocal, but you have to do the work to separate the products from the unreacted reactants, and also separate a product mixture.

Jeremiah Adams · Answer

undefined 1. Precipitate formation; 2. Gas evolution; 3. Color change; 4. Energy release or absorption (heat or light).