Evidence of Chemical. Change

Think back to what you observed in the video of a circuit board sitting in etching solution.  What types of evidence was there that a chemical reaction was taking place?  Base your answer on the list shown here. 

How would someone know, when observing baking soda and vinegar mixing together, that a chemical reaction was taking place? 

If you're ever outside in very cold weather, you can use a product called "HotHands" to warm up.  You take out a special pouch and shake it up, and once it is exposed to air and the chemicals mix, the packet begins to heat up and it can stay warm for hours.  What evidence is there that what is happening inside the packet is a chemical changes? 

This section of the video describes a type of evidence of a chemical reaction called a "precipitate."  

Rewatch this section of video and try to complete this sentence to explain what a precipitate is: 

A precipitate is when two liquids are mixed together and........

Fireworks exploding in the sky happen because of a chemical reaction taking place in the fire cracker. 

Based on what you learned in this video, what are three pieces of evidence you could observe when watching firecrackers to support the claim that a chemical reaction is taking place.