Describe the 2 types of energy changes that can occur in chemical reactions

Endothermic - the molecules require energy to break bonds

exothermic - the molecules or atoms often form bigger molecules and release energy

an exothermic reaction is when heat or gas is released - this is the most common of the two. eg. candle, computer, car

an endothermic reaction is when (usually but not always) heat is stored. An example is an icepack when the coolness is stored