Why is burning wood exothermic? I thought the wood is taking in heat to burn, therefore endothermic. However, it then gives off heat which makes it exothermic. Which is it?
Burning wood in air is an exothermic process (it releases heat), but there is an energy barrier, so it requires a bit of heat in the beginning to get the reactions started.
Wood reacts with oxygen in the air to form (mostly) carbon dioxide and water vapor. The process involves many different individual chemical reactions, and it requires some energy to initiate the reactions. This is because it's usually necessary to break some chemical bonds (endothermic) before new stronger bonds can be formed (exothermic). Overall, though, more heat is released in forming the final products than is consumed in starting new reactions.