One thing that I learned this chapter is that an exothermic reaction is when more energy is given off than taken in. Another thing I learned is that an endothermic reaction is when more energy is taken in than given off. The last thing that I learned this chapter in science is what the pH scale is. It is the acids and bases on a scale from 0 to 14 based on how strong or weak the acid or base is. What I liked best in this chapter was the chemical reaction in a bag which is in the picture because it was cool to see the bag expand and one of the bags in our class popped. What I liked least about this unit was the study guides because I don't like answering like 15 essay questions. The question that I have is how many chemical reactions are there in the world?