Honors Chemistry
Predicting Reactions
There are several reaction types to know. We will be focusing on the following reaction types
· Synthesis
· Decomposition
· Single replacement
· Double replacement
· Combustion
Use the following examples to complete practice problems.
COMBINATION/SYNTHESIS: (SOME REDOX)
1. Two elements → binary compound
metal + nonmetal → salt (ionic – transfer)
nonmetal + nonmetal → molecule (covalent – share)
(except two metals → no reaction)
Ex) 2Na(s) + Cl2(g) → 2NaCl(s)
Ex) S(g) + O2(g) → SO3(g)
2. Nonmetal oxide + water → oxyacid
Ex) H2O(l) + CO2 (g) → H2CO3(aq)
Ex) H2O(l) + SO2 (g) → H2SO3(aq)
3. Active metal oxide + water → metal hydroxide (Group I & II metals only )
Ex) K2O(s) + H2O(l) → 2KOH(aq)
4. Metal + oxygen → metal oxide
Ex) Zn(s) + O2(g) → ZnO(s)
5. Ammonia + acid → ammonium salt
Ex) NH3 (aq)+ HCl(aq) → NH4Cl (aq)
DECOMPOSITION: (SOME REDOX)
1. Metallic carbonates (heated) → metal oxide + carbon dioxide
Ex) CaCO3(s) CaO(s) + CO2(g)
2. Metallic bicarbonates (heated) → metal carbonate + carbon dioxide + water
Ex) 2NaHCO3(s) Na2CO3(s) + CO2(g) + H2O(g)
3. Metallic hydroxide (heated) → metal oxide + water
Ex) Mg(OH)2(s) MgO(s) + H2O(l)
4. Metallic chlorates (heated) → metal chloride + oxygen
Ex) 2KClO3 (s) 2KCl(s) + 3O2(g)
5. Oxyacid (heated) → nonmetal oxide + water
Ex) H2CO3 CO2(g) + H2O(l)
6. Binary compound (heated or electrolyzed) → constituent elements
Ex) 2HgO(s) 2Hg(s) + O2(g)
Ex) 2H2O(s) 2H2(g) + O2(g)
SINGLE REPLACEMENT: (REDOX)
1. Replacement of a metal in a compound by a more active metal
metal + aqueous salt → new metal + new salt
Ex) Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
2. Active metal + water → metal hydroxide + hydrogen
Ex) Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g)
3. Metal + acid → salt (dissolved) + hydrogen gas (bubbles)
Ex) Al(s) + H2SO4 (aq) → Al2(SO4)3(aq) + H2(g)
4. Replacement of a halogen by a more active halogen (*Order on P.T.)
Halogen + aqueous halide salt → new halogen + new halide salt
Ex) Cl2 (g)+ KBr(aq) → KCl(aq) + Br2(l)
METATHESIS (DOUBLE REPLACEMENT)
These reactions begin with two reactant compounds and produce two product compounds. They typically occur when the reactants are acids, bases or salts. The two major classes are metathesis and acid/base reactions.
1. 2 aqueous salts → 2 new salts
Ex) AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)
2. Acid + base (metal hydroxide) → salt + water (neutralization)
Ex) H2SO4 (aq)+ Ca(OH)2(aq) → CaSO4(aq) + H2O(l)
Ex) HC2H3O2(aq) + Al(OH)3(s) → Al(C2H3O2)3(aq) + H2O(l)
3. Acid + salt → new acid + new salt
Ex) HCl(aq) + NaC2H3O2(aq) → NaCl(aq) + HC2H3O2(aq)
Gas Production Double Replacement Reactions: formation of a precipitate and neutralization are both driving forces in a reaction. But the formation of a gas or a weak acid is also a driving force. If a gas or a weak acid can be produced in a double replacement reaction, then it will. You already know your weak acids and some of the more commonly produced gases are:
Common gases:
· H2S
· CO2 This is often predicted as the product H2CO3 but in reality this is CO2 and H2O
· SO2 This is often predicted as the product H2SO3 but in reality this is SO2 and H2O
· NH3 This is often predicted as the product NH4OH but in reality this is NH3 and H2O
4. Acid + metal carbonate (or bicarbonate) → salt + water + carbon dioxide gas
Ex) HCl(aq) + Na2CO3(aq) → NaCl(aq) + H2O(l) + CO2(g)
5. Acid + sulfide salt → salt + hydrogen sulfide gas
Ex) HCl(aq) + K2S(aq) → KCl(aq) + H2S(g)
6. Ammonium salt + metal hydroxide → ammonia gas + salt + water
Ex) NH4Cl(aq) + NaOH(aq) → NH3(g) + NaCl(aq) + H2O(l)
COMPLETE COMBUSTION with Oxygen (REDOX)
1. Hydrocarbon + oxygen gas → carbon dioxide + water
Ex) CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l)