How fire works.

The 2 types of chemical reactions to make a fire is fire that requires heat and fire that give out heat as they work. The wood reacts to the air around it when you set wood on fire. This type of chemical reactions gives off a lot of heat that makes the gasses in the air glow. The glowing gasses is the flame you see. The things that make a flame look the way it does depends on how much air is there to burn, what is being burnt, and heat.