IIIIIIIVV I.Intro to Reactions 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

C. Chemical Equations Pt a catalyst is present (in this case, platinum) (substance dissolved in water)

Diatomic Elements n H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2

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 moles of aluminum metal react with three moles of aqueous copper(II) chloride to produce three moles of copper metal and two moles of aqueous aluminum chloride. How many? Of what? In what state? Al 2(s)(s)+ 3CuCl 2 (aq)  3 Cu(s)(s)+ 2AlCl 3 (aq)

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

IIIIIIIVV II. Balancing Equations

A. Balancing Steps 1.Write the unbalanced equation. 2.Count atoms on each side. 3. Add coefficients to make #s equal. Note: you may not change a subscript Coefficient  subscript = # of atoms 4. Reduce coefficients to lowest possible ratio, if necessary.

B. Helpful Tips n Balance one element at a time. n If an element appears more than once per side, balance it last. n Balance polyatomic ions as single units.  “1 SO 4 ” instead of “1 S” and “4 O”

Al + CuCl 2  Cu + AlCl 3 Al Cu Cl  3  6   C. Balancing Example Aluminum and copper(II) chloride react to form copper and aluminum chloride. 2  2  6

Balancing Equations C 3 H 8 (g) + O 2 (g) ----> CO 2 (g) + H 2 O(g) C 3 H 8 (g) + O 2 (g) ----> CO 2 (g) + H 2 O(g) B 4 H 10 (g) + O 2 (g) ----> B 2 O 3 (g) + H 2 O(g)

Balancing Equations Sodium phosphate and iron (III) oxide react to form sodium oxide and iron (III) phosphate Na 3 PO 4 + Fe 2 O > Na 2 O + FePO 4 Na 3 PO 4 + Fe 2 O > Na 2 O + FePO 4