- Energy Level Diagram is a graph that shows the energy change of a chemical reaction ( graf yang menunjukkan perubahan tenaga dalam tindak balas kimia ) • The energy change can be presented by using a n energy level diagram . (perubahan tenaga boleh diwakili menggunakan rajah aras tenaga) l Energy change, Δ H = energy bond breaking + bond formation l In exothermic reaction, - the heat released from the bond formation is greater than the heat absorbed for bond breaking . - A negative sign for Δ H shows that heat is released l In endothermic reaction, - the heat absorbed from the bond breaking is greater than the heat released for bond forming.