Units 1 and 2 1 Choose the correct option. a) An example of a chemical change is: A melting chocolate B leaving an iron nail to rust C dissolving salt in water D allowing solid air freshener to sublimate b) Which is not a property of physical change? A Atoms and molecules are conserved. B Atoms and molecules are rearranged. C The changes are permanent. D The changes are reversible. c) Which is not a property of chemical change? A A chemical reaction takes place. B There are large changes in energy. C The products have different properties from the reactants. D They are examples of phase changes. d) Which is a wrong statement? A To prove the Law of Constant Composition you add all the atomic masses of atoms in a compound. B The Law of Constant Composition states that all samples of a chemical compound have the same elemental composition. During a chemical reaction the atoms are conserved. C D During a chemical reaction, the sum of the formula masses of the products must equal the sum of the formula masses of the reactants