In this chapter I learned about chemical and physical changes in matter. I also learned about chemical reactions in this chapter. We also learned about endothernic and exothermic energy, but i still can't tell the difference. One more thing we learned about were acids and bases. A strong acid can eat through metal, but most acids are found in foods that we eat such as apples, lemons, and limes. What is the difference between an endothermic reaction and exothermic reaction.