HELPP Select the correct answer. Which method of testing substances is a sure way to identify a chemical reaction? *

A. change in color
B. Change in density

actually it should be a formation of bubbles that identifies a chemical reaction.

asfe afr dsef rfdg fghgnts fhbfgd   hdfdx

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.