the elements in the chemical reaction stays the same after the reaction & oxygen reacts with iron to produce rust ->  iron and oxygen elements stay the same after the reaction  the elements in the chemical reaction stays the same after the reaction & oxygen reacts with hydrogen to produce water ->  oxygen and hyrdrogen elements stay the same after the reaction  iron and oxygen elements stay the same after the reaction & oxygen and hyrdrogen elements stay the same after the reaction -> the elements of two reactions stay the same