Question

Why is the burning of a candle considered to be an irreversible change, even though we get back the wax after cooling it?

Answer 1

Generally, combustion or burning and most chemical reactions, are allirreversible. After burning something, like a candle, it is not possible to restore the original candle in order to burn it again. On the other hand, after wax melts, it solidifies on cooling and can be molten on heating again.