HELP ASAP which of these is an indication that a chemical reaction has occurred?
A.melting of a substance
B. boiling of a substance
C. formation of a precipitate
D.freezing of a subtance
A chemical reaction would be something like a paper burning, a match lighting, etc. A physical reaction is just a change in the appearance. At least partially.
A, B and D are all physical changes. The substance is still that substance and it hasn't changed chemically. The change of state of matter is only a physical change because the substance is still the same as it was in the previous state.
