Comparing the total number of bonds broken to those formed is the first step in helping us determine if a reaction is endothermic or exothermic. On the previous page, you were provided with atom cutouts to better enable you to determine where bonds are located in the reactants and which bonds must be broken to form the products.
Drawing atom models is another way to go about this same process. In the questions below, you will be asked to draw atom models for both the reactants and the products in each chemical reaction. Then you will count both the bonds present in the reactants that must be broken in order to form the products, and the number of new bonds that must be formed to create the products.
You will then use the difference in the number of bonds broken vs. formed to determine if the overall chemical reaction is likely endothermic or exothermic. More bonds broken than formed correlates with an endothermic reaction as more energy must be added to the system to break the bonds, while fewer bonds broken than formed correlates with an exothermic reaction. An exothermic reaction is one is which energy is being released from the system.
