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.
Example: 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? 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 = “unit” 3 molecules of carbon dioxide 2 atoms of magnesium 4 units of magnesium oxide 3CO 2 2Mg 4MgO
Example to produce How many? Of what? In what state? Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g) One atom of solid zinc reacts with two molecules of aqueous hydrochloric acid one unit of aqueous zinc chlorideand one molecule of hydrogen gas.
IIIIIIIVV II. Balancing Equations Chemical Reactions
A. Balancing Steps 1.Write the unbalanced equation. 2.Count atoms on each side. 3.Add coefficients to make #s equal. Coefficient subscript = # of atoms 4.Reduce coefficients to lowest possible ratio, if necessary. 5.Check yourself before you wreck yourself
B. Helpful Tips n one element at a time. n Update ALL atom counts after adding a coefficient. n If an element appears more than once per side, balance it last.
Al + CuCl 2 Cu + AlCl 3 Al Cu Cl 1 1 1 1 2 3 2 3 6 3 33 2 C. Balancing Example Aluminum and copper(II) chloride react to form copper and aluminum chloride. 2 2 6
IIIIIIIVV Chemical Reactions III. Types of Chemical Reactions
A. Combustion CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) n the burning of any substance in O 2 to produce heat A + O 2 B
Na(s)+ O 2 (g) C 3 H 8 (g)+ O 2 (g) 5 3 4 n Products: contain oxygen hydrocarbons form CO 2 + H 2 O CO 2 (g)+ H 2 O(g) Na 2 O(s) 4 2
B. Synthesis n the combination of 2 or more substances to form a compound n only one product A + B AB