In what ways is the compound formed of iron and oxyge. different from a mixture of iron and oxygen

This can be explained by determining the difference between a compound and a mixture. In a compound, the elements are chemically combined meaning that they are sharing chemical bonds and therefore can only be chemically separated through a reaction. The elements in the mixture are only physically mixed and do not share chemical bonds. The elements can, therefore, be physically separated without a  reaction.  

i do not get it   at all

definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.