IIIIIIIVV I.Intro to Reactions (p. 282 – 285) Ch. 9 – Chemical Reactions

A.Signs of a Chemical Reaction n Evolution of heat and light n Formation of a gas n Formation of a precipitate n Color change

B.Law of Conservation of Mass n mass is neither created nor destroyed in a chemical reaction 4 H 2 O 4 H 2 O 4 g32 g 36 g n total mass stays the same n atoms can only rearrange

C. Chemical Equations A+B C+D REACTANTSPRODUCTS

p. 283 C. Chemical Equations

D. Writing Equations n Identify the substances involved. n Use symbols to show: 2H 2 (g) + O 2 (g) 2H 2 O(g) How many? - coefficient Of what? - chemical formula In what state? - physical state n Remember the diatomic elements!

D. Writing Equations Two atoms of aluminum react with three units of aqueous copper(II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride. How many? Of what? In what state?

E. Describing Equations n Describing Coefficients: individual atom = atom covalent substance = molecule ionic substance = unit 3 molecules of carbon dioxide 2 atoms of magnesium 4 units of magnesium oxide 3CO 2 2Mg 4MgO

E. Describing Equations How many? Of what? In what state? Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g)