Chemical Reactions *5 General Types Combination Decomposition Single-Replacement Double-Replacement Combustion

Some exceptions Some reactions may appear to fit into more than one category

Combination Reactions AKA – Synthesis Occurs when 2 or more substances combine to form a single substance Reactants are typically 2 elements or 2 compounds Product is always a compound

Group A metals react with a nonmetal – get metal cation and nonmetal anion 2Na(s) + Cl2(g) 2NaCl(s)

Two nonmetals react to form more than one compound C(s) + O2(g) CO2(g) 2C(s) + O2(g) 2CO(g)

Transition metals reacting with nonmetals may give more than one product 4Cu(s) + O2(g) 2Cu2O copper (I) oxide 2Cu(s) + O2(g) 2CuO copper (II) oxide

Some nonmetal oxides react with water to form an acid CO2(g) + H2O H2CO3(aq) Carbonic acid

Some metal oxides react with water to give a base (contains hydroxide ions) CaO(s) + H2O(l) Ca(OH)2(aq) Calcium hydroxide

Practice Mg + O Ca + S N2O5 + H2O 2Mg + O2 2MgO Ca + S CaS N2O5 + H2O 2HNO3

Decomposition Reactions Single compound breaks down into 2 or more products Products can be any combination of elements and compounds CaCO3(s) heat CaO(s) + CO2(g)

Hard to predict products of decomposition reaction, unless it’s a binary compound Breaks down into constituent elements Often requires energy in form of heat, light or electricity

Extremely rapid decomposition reactions produce gases and heat Often cause explosions Example: dynamite

Practice Ag2O(s) Nickel(II) Carbonate Nickel(II) oxide + ? 2AgO(s) 4Ag(s) +O2(g) NiCO3 NiO + CO2 (g)

Single-Replacement Reactions Add Na to water = violent reaction Produces H2 can ignite This is a single-replacement reaction: One element replaces a second element in a compound AKA: single-displacement reaction

2Na(s) + 2H2O(l) H2(g) + 2NaOH(aq)

Whether a metal replaces another metal in a reaction is determined by relative reactivities. The activity series of metals lists metals in order of decreasing activity. A reactive metal will replace any metal listed below it on the chart.

K replaces Na, Al, or Zn Fe will not replace Mg, Ca, or Li K(s) + NaNO3(aq) KNO3(aq) + Na(s) Fe(s) + Ca(NO3)2(aq) no reaction

Nonmetals can also replace nonmetals Limited to halogens Activity decreases as you go down the family

Practice Ag(s) + KNO3(aq) Zn(s) + AgNO3(aq) No reaction Zn(NO3)2(aq) + 2Ag(s)

Double-Replacement Reaction When ionic solids dissolve in water- form homogeneous mixtures. If 2 or more ionic solutions are mixed: A) get aqueous homogeneous mixtures B) chemical reaction will occur

K2CO3(aq) + BaCl2(aq) 2KCl(aq) + BaCO3(s) A reaction occurred- white precipitate formed

Double-replacement reactions involve exchange of positive ions between reacting compounds One product precipitates from solution One product is a gas that bubbles out One product is a molecular compound like water

Practice HCl(aq) + Ca(OH)2(aq) 2HCl(aq) + Ca(OH)2(aq) CaCl2(aq) + 2H2O(l) Ag2SO4(aq) + AlCl3(aq) 3Ag2SO4(aq) + 2AlCl3(aq) 6AgCl(s) + Al2(SO4)3(aq)

Combustion Reactions Element or compound reacts with oxygen Usually produces energy as heat & light Usually involves hydrocarbons (hydrogen & carbon)

Complete combustion yields CO2 + H2O Incomplete combustion (lack of O2) may also yield C and CO 2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(g)

Reactions between some elements + O2 are also combustion reactions 2Mg(s) + O2(g) 2MgO(s) This can also be classified as a combination reaction

Practice Complete combustion of C4H8 Butane C4H8 + 6O2 4CO2 + 4H2O Complete combustion of C8H18 Octane 2C8H18 + 25O2 16CO2 + 18H2O

Exceptions Some reactions don’t fit any of these five types Example- Oxidation-reduction reaction (discussed in chapter 20)