You are only allowed to ask one question at a time so I edited down accordingly. The chemical kinetics profile for a reaction measures its energy over time. More specifically, it traces the energy levels of the reactants as they are converted to products over the course of the chemical reaction at the molecular level. For the combustion of wood, we have wood being converted to carbon dioxide and water vapor (in a theoretical scenario of complete combustion). The products are more thermodynamically stable than the wood reactant, thus they are at a lower energy level and the reaction is exothermic (meaning it gives off heat). This certainly is true and readily apparent with wood burning. But in order to get from reactant to products, an energy barrier must be overcome for the reaction to occur, otherwise the reaction would spontaneously occur and this is certainly not the case. The energy barrier is called the activation energy. The spark or flame required to start wood burning provides the energy required to overcome the activation energy barrier and allows the wood to burn and become the products.