Question

How does a fire actually help magnesium react with oxygen to form magnesium oxide????????

Answer 1

Fire increase chemicals' energy, so the ratio of chemicals having energy more than the activation energy increases.

Explanation:

Fire help to increase the temperature when reacting.
To have a reaction, each chemicals need to have proper kinetic energy and have efficient collision. When temperature increase, chemicals' that has energy larger than activation energy increases which accelerates reaction. Without fire, chemicals'(especially oxygen's) energy won't reach to activation energy. The amount of reaction is so small that reaction can't be observed.