Q:
A: What appears to us as fire is electrons jumping between the atoms/molecules of oxygen and material you are burning. This reaction usually gives off energy as heat. In a manner of saying you may measure the heat from what you see as fire in "joules". This is the unit of energy. Since fire is just oxidation (forming of molecules containing oxygen from molecules which do not have oxygen) it does not have any weight/volume/mass. In a way a spark of electricity is nothing different from a flame. Transfer/Sharing of electrons releases packets of energy called photons. This is what we observe or feel as light. In a flame a photon carries less energy than in a spark.