Bellringer/6.1 Notes (#2 in Notebook) Methane, CH4, is an organic compound that is the principal component of natural gas. Many people burn methane when cooking or heating homes. The chemical reaction of methane burning is shown in several ways below. What else besides water and carbon dioxide is produced in this reaction that makes methane useful for cooking and heating? Complete the table below with the number of atoms of each element before and after the reaction. How does the number of atoms of each element on the left side of the equation compare to the number on the right? What law does this demonstrate? Use your answer to item 1 and the law of conservation of energy to guess whether there is more energy stored in the bonds among the atoms before the reaction or among the bonds of the atoms after the reaction.

CO2 + H20 → C6H12O6 + O2 I. Chemical Reactions Change Substances Occur when substances undergo chemical changes to form new substances Signs of a chemical reaction: Release of a gas Change in color Heat is emitted B. Chemical reactions consist of two parts: Reactants – on the left (about to react) 2. Products – on the right (newly formed substances) CO2 + H20 → C6H12O6 + O2 Reactants Products

C. Chemical reactions need energy to start The sun provides energy needed for photosynthesis to occur The energy is used to break the bonds between CO2 + H20 D. Chemical reactions can release energy – called an exothermic reaction Any reaction in which combustion takes place would be an exothermic reaction E. Chemical reactions can absorb energy – called an endothermic reaction Photosynthesis is an endothermic reaction b/c more energy is required to break the bonds of the reactants than is formed by the bonding of the products