the lime stone decomposes completely at 1273k but the temperature inside the klin rises to 1473k why?

Answer 1

Well, in "combustion," it's safe to say that whatever you heat with fire is also reacting with oxygen. I am assuming also, when you heat limestone, you are severing the bonds that hold its chemical composition, which is why it can either melt or sublime. Now, if this is true, then the reason the internal heat of the kiln may be higher is because the reaction taking place is exothermic, and it gives out a great deal of heat. This is just a hypothesis, don't take this entirely for an answer...but it should help get things going.