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

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? 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 

E. Describing Equations 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 C. Johannesson II. Balancing Equations Chemical Reactions

C. Johannesson A. Balancing Steps 1.Write the unbalanced equation. 2.Element Inventory, 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.Double check atom balance!!!

C. Johannesson B. Helpful Tips n Balance 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. n Balance polyatomic ions as single units.  “1 SO 4 ” instead of “1 S” and “4 O”

C. Johannesson 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

IIIIIIIVV C. Johannesson Chemical Reactions III. Types of Chemical Reactions

C. Johannesson 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

C. Johannesson Na(s)+ O 2 (g)  C 3 H 8 (g)+ O 2 (g)  A. Combustion n Products:  contain oxygen  hydrocarbons form CO 2 + H 2 O CO 2 (g)+ H 2 O(g) Na 2 O(s) 4 2

C. Johannesson B. Synthesis n the combination of 2 or more substances to form a compound n only one product A + B  AB

C. Johannesson B. Synthesis H 2 (g) + Cl 2 (g)  2 HCl(g)

C. Johannesson Al(s)+ Cl 2 (g)  AlCl 3 (s) B. Synthesis n Products:  ionic - cancel charges  covalent - hard to tell

C. Johannesson C. Decomposition n a compound breaks down into 2 or more simpler substances n only one reactant AB  A + B

C. Johannesson C. Decomposition 2 H 2 O(l)  2 H 2 (g) + O 2 (g)

KBr(l)  K(s) + Br 2 (l) 2 2 C. Decomposition n Products:  binary - break into elements

C. Johannesson D. Single Replacement n one element replaces another in a compound  metal replaces metal (+)  nonmetal replaces nonmetal (-) A + BC  B + AC

C. Johannesson D. Single Replacement Cu(s) + 2AgNO 3 (aq)  Cu(NO 3 ) 2 (aq) + 2Ag(s)

C. Johannesson Fe(s)+ CuSO 4 (aq)  Cu(s)+ FeSO 4 (aq) D. Single Replacement n Products:  metal  metal (+)  nonmetal  nonmetal (-)

C. Johannesson AB + CD  AD + CB E. Double Replacement n ions in two compounds “change partners” n cation of one compound combines with anion of the other

C. Johannesson E. Double Replacement Pb(NO 3 ) 2 (aq) + K 2 CrO 4 (aq)  PbCrO 4 (s) + 2KNO 3 (aq)

Pb(NO 3 ) 2 (aq)+ KI(aq)  PbI 2 (s)+ KNO 3 (aq) E. Double Replacement n Products:  switch negative ions 2 2