When we learned about Changes in Matter, I learned  what exothermic and endothermic reactions are. An exothermic reaction is a reaction that releases energy in a chemical reaction. An endothermic reaction is a reaction that heat energy is absorbed in a chemical reaction. I also learned what the pH scale is. The pH scale is a set of number between 0 and 14 used to measure the stength of acids and bases. What I liked the best about this unit was all the labs we did. What I did not like about this unit is all the work. One question I had was what is neutralization is?