Double Displacement (or Replacement) Reactions

• Also referred to as metathesis reaction The two compounds exchange ions to produce two

new compounds. It is easier to simply remember that the cations (+ ions) exchange anions (- ions).

AB + CD CB + ADNOTE: always write the cation first then the anion.• Many reactions including precipitation and

neutralization use the double displacement mechanism.

pp. 220, 223

Double Displacement (or Replacement)

Reactions

Fig. 8-18, p. 221

NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)

Double Displacement (or Replacement) Reactions

• PREDICT THE PRODUCT & BALANCE

1. MgSO4 + LiOH ___________

2. Pb(NO3)2 + Na2CO3 ____________

3. HNO3 + Ba(OH)2 ___________

Answers are on the next slide.

Double Displacement (or Replacement) Reactions

• ANSWERS

1. MgSO4 + 2 LiOH Mg(OH)2 + Li2SO4

2. Pb(NO3)2 + Na2CO3 PbCO3 + 2 NaNO3

3. 2 HNO3 + Ba(OH)2 Ba(NO3)2 + 2 H2O

Exchange cations

PRECIPITATION REACTIONPRECIPITATION REACTIONA reaction where an insoluble solid is formed during a

reaction between two aqueous solutions.

(aq) (aq) + + (aq)(aq) (aq)(aq) + + (s)(s)

2KI(aq) + Pb(NO3)2(aq) 2KNO3(aq) + PbI2(s)

NEUTRALIZATION REACTIONNEUTRALIZATION REACTIONA reaction between an acid and a base which results in the

production of a salt and water.

HA + BOH (metal/nonmetal) + H2O

HNO3(aq) + KOH(aq) KNO3(aq) + H2O(l)

Exchange cationsExchange cations

Table 9-3, p. 252

Fig. 9-13, p. 253

Single Displacement (or Replacement) Reactions

One element reacts with a compound to produce a different element and a new compound.

A + BC AC + B• NOTE: if the element is a metal, it will replace the cation.

A + BC C + BA• NOTE: if the element is a nonmetal, it will replace the anion.

Many reduction-oxidation reactions use the single displacement mechanism.

pp. 218, 220

Single Displacement (or Replacement)

Reactions

Fig. 8-15, p. 218

Single Displacement (or Replacement) Reactions

PREDICT THE PRODUCT

1. Ca + HCl

2. ZnBr2 + I2

3. Cu + AgNO3

Answers are on the next slide.

Single Displacement (or Replacement) Reactions

ANSWERS:

1. Ca + 2 HCl CaCl2 + H2

2. ZnBr2 + I2 ZnI2 + Br2

3. Cu + 2AgNO3 2Ag + Cu(NO3)2

Fig. 9-9, p. 245

A reaction occurs when a piece of zinc is dipped into a solution of copper (II) nitrate. Write the conventional (molecular), ionic and net ionic equations.

Single-Replacement Redox Reactions

• Conventional (Molecular) Equation

Zn(s) + Cu(NO3)2 (aq) → Zn(NO3)2(aq) + Cu(s)

• Ionic EquationZn(s) + Cu+2

(aq) + NO3- (aq) → Zn+2

(aq) + NO3- (aq) + Cu(s)

• Net Ionic EquationZn(s) + Cu+2

(aq) → Zn+2(aq) + Cu(s)

Single-Replacement Redox Reactions

Table 9-2, p. 245

• What happens if we place a piece of copper metal into a solution of zinc nitrate?

• Evidence shows that copper is below zinc on the Activity Series, therefore copper will not replace zinc and no reaction occurs.

• Cu(s) + Zn(NO3)2(aq) → NR

Single-Replacement Redox Reactions

ReductionReduction--OxidationOxidation Reactions ReactionsA reaction in which electrons are transferred from one A reaction in which electrons are transferred from one

species to anotherspecies to another..

• Oxidation means the loss of electrons

• Reduction means the gain of electrons

Rusting is a redox reaction:

4Fe (s) + 3O2 (g) 2Fe2O3 (s)

As a reactant Fe has a zero oxidation state but as a product (in Fe2O3) iron has a 3+ oxidation state. Three electrons per atom had to be transferred (lost) in order for this to happen. Note that oxygen also changed from a zero oxidation state to a 2- oxidation state. Oxygen needed to gain 2 electrons per atom.

ReductionReduction--OxidationOxidation Reactions Reactions• Oxidation means the loss of electrons

• Reduction means the gain of electrons

Electrochemistry involves redox Rx.Cu(s) + 2AgNO3(aq) 2Ag(s) + Cu(NO3)2(aq)

The reactant Cu has a zero oxidation state (all elements have a zero oxidation state) but as a product, in Cu(NO3)2,the copper atom loses two electrons and has a 2+ oxidation state. The other atom which acquired the electrons donated by copper is silver. As a reactant silver has a 1+ oxidation state then by gaining electrons from copper, the ions are turned into elemental silver with a zero oxidation state.

The net effect of this reaction has metallic copper being The net effect of this reaction has metallic copper being oxidizedoxidized to to copper ions and silver ions being copper ions and silver ions being reduced reduced to silver metalto silver metal.

Fig. 16-2, p. 459

COMBINATION REACTIONCOMBINATION REACTIONA reaction in which two or more substances

combine to form a single product.

A +B + CA +B + C ABC ABC

CaO(s) + SOCaO(s) + SO22(g) (g) CaSO CaSO33(s)(s)

Fig. 8-11, p. 214

C (s) + O2 (g) → CO2 (g)

DECOMPOSITION REACTIONDECOMPOSITION REACTIONA reaction in which a single compound reacts to

give two or more substances, usually requiring a raise in temperature.

ABCABC A + B + C A + B + C

2KClO2KClO33(s) (s) 2KCl(s) + 3O 2KCl(s) + 3O22(g)(g)

Fig. 8-13, p. 215

2H2O(l) → 2H2(g) + O2(g)

COMBUSTION REACTIONCOMBUSTION REACTIONA reaction of a substance with oxygen, usually the rapid

release of heat produces a flame.

CH + OCH + O22 CO CO22 + H + H22OO

2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g)

(hint: balance the C’s first, followed by the H then the O’s)

Many times in a combustion reaction, heat energy is given off. In chemical terms this is called an exothermic reaction. Thermochemistry is field of chemistry which studies the transfer of heat in a reaction.

The thermodynamic equation representing this exothermic reaction is:

2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g) + heat (in Joules)

GAS FORMATION REACTIONSGAS FORMATION REACTIONS• A reaction that produces a gas from reactants

not in the gaseous state. 2 HCl (aq) + ZnS (s) ZnCl2 (aq) + H2S (g)

Zn (s) + 2 HCl (aq) ZnCl2 (aq) + H2 (g)

• Many gas formation reactions involve two steps, first the double displacement reaction then the decomposition reaction of an unstable substance.

NaNa22COCO33 + 2HCl + 2HCl 2 NaCl + H 2 NaCl + H22COCO33

HH22COCO3 3 CO CO22 + H + H22OO

• Besides carbonic acid (H2CO3), sulfurous acid (H2SO3) also decomposes into SO2 and water.

COMMON GAS FORMATION COMMON GAS FORMATION REACTIONS YOU SHOULD REMEMBERREACTIONS YOU SHOULD REMEMBER

• NH4OH → NH3 (g) + H2O (l)

• H2CO3 → CO2 (g) + H2O (l)

• H2SO3 → SO2 (g) + H2O (l)

Table 8-3, p. 223

GROUP STUDY PROBLEM # 17aGROUP STUDY PROBLEM # 17aWrite the following as balanced chemical equations then classify each reactionWrite the following as balanced chemical equations then classify each reaction ..

1. Solid mercuric oxide decomposes at high temperatures to form metallic mercury and oxygen.

2. Aqueous lead(II) nitrate reacts with aqueous magnesium bromide to produce the insoluble salt lead(II)bromide and soluble magnesium nitrate.

3. At room temperature, aqueous ammonium carbonate is added to hydrochloric acid to produce aqueous ammonium chloride, water and carbon dioxide.

4. Hydrochloric acid is poured over tin metal producing hydrogen gas and tin (IV) chloride.

5. The combustion of ethanol, C2H5OH, results in the production of carbon dioxide and water.

PRACTICE PROBLEMS # 17aPRACTICE PROBLEMS # 17aWrite the following as balanced chemical equations then classify each reactionWrite the following as balanced chemical equations then classify each reaction ..

1. Magnesium metal is combined with nitrogen at elevated temperatures to form magnesium nitride powder.

2. An aqueous solution of soluble aluminum nitrate is mixed with aqueous sodium hydroxide to produce insoluble aluminum hydroxide and a sodium nitrate solution.

3. Solid potassium sulfite is added to hydrochloric acid to produce sulfur dioxide, water, and potassium chloride.

4. Acetic acid reacts with calcium hydroxide to produce calcium acetate and water.

5. Lithium metal is dropped in water to produce lithium hydroxide and hydrogen gas.

3 Mg (s) + N2 (g) Mg3N2 (s); combination, redox

Al(NO3)3 (aq) + 3NaOH (aq) Al(OH)3(s) + 3NaNO3(aq) ; ppt, DD

K2SO3 (s) + 2HCl (aq) H2SO3 (aq) + 2KCl (aq) ; DD then

H2SO3 (aq) H2O (l) + SO2 (g) ; decomposition

overall Rx : K2SO3 (s) + 2HCl (aq) H2O (l) + SO2 (g) + 2KCl (aq)

2 HC2H3O2 (aq) + Ca(OH)2 (aq) Ca(C2H3O2)2 (aq) + 2H2O (l) ; DD, neutralization

2Li (s) + 2H2O(l) 2LiOH (aq) + H2 (g); SD, redox

GROUP STUDY PROBLEM # 17bGROUP STUDY PROBLEM # 17bPREDICT THE PRODUCT THEN WRITE A BALANCED EQUATION FOR EACH REACTIONSPREDICT THE PRODUCT THEN WRITE A BALANCED EQUATION FOR EACH REACTIONS ..

1. The reaction between lead (II) acetate and ammonium carbonate solutions results in the formation of a white solid.

2. An zinc metal wire is dipped in hydrobromic acid.

3. The decomposition of sulfurous acid.

4. Sodium hydroxide solution is added to sulfuric acid.

5. Solid tin(II) sulfide is added to hydroiodic acid.

PRACTICE PROBLEMS # 17bPRACTICE PROBLEMS # 17bPREDICT THE PRODUCT THEN WRITE A BALANCED EQUATION FOR EACH REACTIONSPREDICT THE PRODUCT THEN WRITE A BALANCED EQUATION FOR EACH REACTIONS ..

1. Cadmium (II) iodide solution is added to aqueous potassium phosphate.

2. Magnesium hydroxide solution is mixed with phosphoric acid.

3. The decomposition of carbonic acid.

4. The combustion of methanol, CH3OH.

5. Solid cadmium reacts with a copper(II) sulfate solution.

3 CdI2 (aq) + 2 K3PO4 (aq) Cd3(PO4)2 (s) + 6 KI (aq)

3 Mg(OH)2 (aq) + 2 H3PO4 (aq) Mg3(PO4)2 (aq) + 6 H2O (l)

H2CO3 (aq) CO2 (g) + H2O (l)

2 CH3OH (l) + 3 O2 (g) 2 CO2 (g) + 4 H2O (l)

Cd (s) + CuSO4 (aq) Cu (s) + CdSO4 (aq)