"And bond breaking (fission) is endotherimic........."
When we combust a hydrocarbon to get energy (to warm the house for instance), we have to break strong C-H, C-C, and O=O bonds; such a process requires energy.
Upon complete combustion, we MAKE STRONGER C=O and O-H bonds in the combustion products, CO_2 and H_2O; such a process RELEASES energy, which we can use to heat our homes, or drive a motor. And the enthalpy or energy change of a reaction can be precisely measured:
CH_4(g) + 2O_2(g) rarr CO_2(g) + 2H_2O(l) + Delta
In the given reaction, we have to break STRONG C-H and O=O bonds. Such a process requires energy. But we make STRONGER C=O and O-H bonds. The balance, the energy difference is the enthalpy of reaction represented as Delta (and quoted as a NEGATIVE value if heat is released!).
