How do you know when there has been a chemical reaction?
New chemical substances will form. There are a number of key things to look for to know if new chemicals are being formed.
Here's what to look for... you don't need to see all of these things to know a chemical reaction happened.
Permanent color change - like when an iron nail rusts (iron reacts with oxygen)
Formation of a precipitate (a solid forms when two liquid solutions are combined)
Formation of a gas - bubbles (must be a newly formed gas, bubbles formed when water boils doesn't count because they are just water in a different state of matter - gas rather than liquid
Temperature change - gives off heat (burning something) or absorbs energy (reaction in an instant ice pack)
Try figuring out which changes in this video are chemical changes and which are physical changes...
Hope this helps!