Ch. 2.4 Chemical Reactions

Chemical Property  Chemical property: the ability of a substance to undergo a specific chemical change.  Example: Iron binds Oxygen to form rust Ability to rust is a chemical property of iron Fe + O → FeO (rust)

Chemical Reaction  During a chemical change, the composition of matter always changes. Also called a chemical reaction  Substance(s) is change(s) into new substance(s).  Reactant—substance present at start of the reaction.  Product—substance produced in the reaction.

Chemical Rx Fe + O → FeO Reactant(s): ________ Product(s): _________ Arrow indicates chemical change

Recognizing Chemical Changes  Possible clues include…  heat production  a change in color  the production of gas  the production of a precipitate  Every chemical change involves a transfer of energy.

Proof of Chemical Change  Samples must be tested before and after the change

Conservation of Mass  During any chemical reaction, the mass of the products is always equal to the mass of the reactants.  Mass is also constant during physical changes.

Law of Conservation of Mass  In any physical change or chemical reaction, mass is conserved.  Mass is cannot be created or destroyed!!!!  If mass of product is less than the sum of reactants often the missing mass “escaped” in form of gas, or vapor