Imagine a campfire on a cold day. At first, the temperature of each log is as cold as the air around it. A few hours after the fire has burned out, the temperature of the ashes will also be cold. But in between, when the fire is burning, the temperature of the logs and surrounding air is very hot. What is the source of this thermal energy? For the answer, begin by identifying the reactants and products for the overall chemical reaction of burning wood. Wood is mostly carbohydrates, the bulk of which is cellulose. Cellulose is made up of hundreds to thousands of glucose groups connectected by oxygen molecules. The chemical formula for cellulose is (C6H12O6)n, where n is the number of glucose groups. For more manageable models, carbohydrates will be modelled as glucose with a chemical formula of C6H12O6.