Hi, I have some silly questions about combustion and the Wikipedia page (http://en.wikipedia.org/wiki/Combustion) doesn't explain all I would like to know. Can you please help to answer these questions? Q1. What exactly makes combustion an exothermic reaction? Is it because there is a tiny loss of mass which had been converted into energy under the form of light & heat? Q2. From the Chemical Equation: CH4 + 2 O2 → CO2 + 2 H2O What had happened between the atoms and molecules so that heat was produced? Q3. Put a sheet of paper on an anvil and slam on it with a hammer. In spite of the great supplement of energy added to the paper at the point of impact, the combustion could not be initiated. Why? Q4. What are the conditions for a material to be combustible? Burning a rock with a flame, like in a camp fire and the rock is just warmed up but still remains a rock. Ultimately, if I use higher temperature, the rock will probably melt but I guess it took more energy to melt the rock than the energy I could recuperate from the melting rock. So what are the condition to be a good combustible? Thanks in advance for any advice.