I. Types of Chemical Reactions () Ch. 9 – Chemical Reactions I. Types of Chemical Reactions ()

Symbols used in equations the arrow separates the reactants from the products  Read “reacts to form” The plus sign = “and” (s) after the formula -solid (g) after the formula -gas (l) after the formula –liquid (aq) dissolved in water

CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) A. Combustion the burning of any substance in O2 to produce heat A + O2  B CH4(g) + 2O2(g)  CO2(g) + 2H2O(g)

Reactants Must Come In Contact with Each Other Molecules and atoms of the reactants must come into contact with each other for a reaction to take place. Example: When a safety match is lighted. One reactant, potassium chlorate (KClO3) is on the match head. The other reactant, phosphorus, P4, is on the striking surface of the matchbox. The reaction begins when the two substances come together by rubbing the match head across the striking surface. If the reactants are kept apart, the reaction will not happen.

A. Combustion 4Na(s)+ O2(g)  2Na2O(s) C3H8(g)+ O2(g)  5 3 4 Products: contain oxygen hydrocarbons form CO2 + H2O 4Na(s)+ O2(g)  2Na2O(s) C3H8(g)+ O2(g)  5 3 4 CO2(g)+ H2O(g)

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

B. Synthesis H2(g) + Cl2(g)  2 HCl(g)

Al(s)+ Cl2(g)  2 3 2 AlCl3(s) B. Synthesis Products: ionic - cancel charges covalent - hard to tell Al(s)+ Cl2(g)  2 3 2 AlCl3(s)

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

C. Decomposition 2 H2O(l)  2 H2(g) + O2(g)

C. Decomposition 2 2 KBr(l)  K(s) + Br2(l) Products: binary - break into elements others - hard to tell 2 2 KBr(l)  K(s) + Br2(l)

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

Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s) D. Single Replacement Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s)

D. Single Replacement Fe(s)+ CuSO4(aq)  Cu(s)+ FeSO4(aq) Products: metal  metal (+) nonmetal  nonmetal (-) free element must be more active (check activity series) Fe(s)+ CuSO4(aq)  Cu(s)+ FeSO4(aq) Br2(l)+ NaCl(aq)  N.R.

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

Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(s) + 2KNO3(aq) E. Double Replacement Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(s) + 2KNO3(aq)

E. Double Replacement Pb(NO3)2(aq)+ KI(aq)  2 2 PbI2(s)+ KNO3(aq) Products: switch negative ions one product must be insoluble (check solubility table) Pb(NO3)2(aq)+ KI(aq)  2 2 PbI2(s)+ KNO3(aq) NaNO3(aq)+ KI(aq)  N.R.