Answer:
See explanation
Step-by-step explanation:
According to the first law of thermodynamics, energy can neither be created nor destroyed, but can be transformed from one form to another.
The thermal energy observed in the hot air while the fire rages is obtained from the chemical energy stored in carbohydrates(cellulose) that compose the wood material. As the wood is burnt, this chemical energy stored in chemical bonds of the wood material is converted to heat. The chemical reaction in the combustion of wood can be simply modeled as the combustion of n moles of glucose.
nC6H12O6(s) + 6nO2(g) ===> 6nCO2(g) + 6nH2O(g)
Note that n may even be thousands of glucose molecules that combine to form cellulose present in wood.