Chemical Reactions Chapter 11

Reactions Reactants Products

Chemical Changes Indications of a chemical change Transfer of Energy Change in temperature Production of Light Formation of a gas Formation of a precipitate (solid) Change in color

Balancing Reactions Reactions must maintain conservation of mass, charge, and energy Reactants and Products must have the same number of atoms of each element 2 H2 + O2  2 H2O Total mass of Reactants must equal the total mass of Products

Balancing Reactions Reactions must maintain conservation of mass, charge, and energy Reactants must have the same total charge as Products Cu+1 + Fe+3  Cu+2 + Fe+2

Balancing Reactions To balance a reaction: Do NOT change chemistry (compounds, subscripts) Only change coefficients (big numbers in front of chemicals) Coefficients can only be whole numbers Must be simplest whole number ratio 2 H2 + O2  2 H2O

Balancing Reactions 4 Na + O2  2 Na2O 2 Al + 3 Br2  2 AlBr3 4 Ni + 3 O2  2 Ni2O3 2 HNO3 + Ca(OH)2  Ca(NO3)2 + 2 H2O

Reaction Types Synthesis Decomposition Single Replacement Double Replacement

Synthesis Chemical change in which two or more substances react to form a single new substance (1 product) Also called Combination A + B  AB 2Mg + O2  2MgO

Synthesis Examples 2 Ca + O2  2 CaO 2 Na + F2  2 NaF 4 K + O2  2 K2O Mg + Cl2  MgCl2

Decomposition Chemical change in which a single compound breaks down into two or more simpler products 1 reactant AB  A + B 2NaCl  2Na + Cl2

Decomposition Examples 2 Fe2O3  4 Fe + 3 O2 2 H2O  2 H2 + O2 2 Na3N  6 Na + N2 2 KI  2 K + I2

Single Replacement Chemical change in which one element replaces a second element in a compound Metal replaces metal (hydrogen included) Nonmetal replaces nonmetal A + BC  AC + B A + BC  BA + C Zn + 2HCl  ZnCl2 + H2

Single Replacement Examples Zn + CuSO4  Cu + ZnSO4 4 Al + 3 TiCl4  3 Ti + 4 AlCl3 3 Ag + AuCl3  Au + 3 AgCl 3 Mg + 2 AlPO4  2 Al + Mg3(PO4)2

Double Replacement Chemical change involving an exchange of positive ions between compounds AB + CD  AD + CB AgNO3 + NaCl  NaNO3 + AgCl

Double Replacement Examples NaCl + AgNO3  NaNO3 + AgCl K2S + CdCl2  2 KCl + CdS K2SO4 + BaCl2  2 KCl + BaSO4 3 NH4OH + AlCl3  3 NH4Cl + Al(OH)3

Spontaneous Reactions A single replacement reaction will only occur if: The single element in the reactants is more active than the element it replaces in the compound

Table J The more active element: Does not want to be alone Wants to be combined with someone else

Spontaneous or not? ZnCO3 + Mg  MgCO3 + Zn PbSO4 + Mn  MnSO4 + Pb 3KNO3 + Al  Al(NO3)3 + 3K 2HCl + Zn  ZnCl2 + H2 2NaBr + I2  2NaI + Br2 YES YES NO YES NO

Spontaneous Reactions A double replacement reaction will only occur if: A precipitate (solid) is produced A liquid is produced H2O(l) A gas is produced

Table F

Spontaneous or not? NaCl + AgNO3  NaNO3 + AgCl K2CO3 + MgSO4  K2SO4 + MgCO3 NH4OH + NaNO3  NaOH + NH4NO3 Yes Yes No