what are the five chemistry equations we need to know for the jc?
There aren't really specific ones. I think you have to learn them all, unfortunately.
I think the most important chemistry equations for the JC is found in the ''Acids and Bases'' and ''Atmosphere'' chapters. Try and look over the balancing equations such as: HCl + NaOH = NaCl + H2O, and also look at what happens when an acid meets a carbonate and when an acid meets a metal in your science textbook. Also, look at the chemical equations for producing oxygen (2H2O2 = 2H2O + O2 (catalyst was MnO2)) and for producing carbon dioxide (2HCl + CaCO3 = CaCl2 + CO2 + H2O). It's also likely you will have to learn the word equations. I have looked at past exam papers, and equations that are to do with those two chapters are essential.
Hope this helps :)