Types of Chemical Reactions

Types of Chemical Reactions

• We will learn 5 types of chemical reactions:1. Synthesis reactions2. Combustion reactions3. Decomposition reactions4. Single-Replacement reaction5. Double-Replacement Reactions• Reactions that form a precipitate• Reactions that form water

– Acid/Base or Neutralization Reactions• Reactions that form a gas

Aqueous Reactions

Synthesis Reaction

• When 2 or more elements or compounds react to form a single product.

• A + B AB• Example:– Sodium combines with chlorine to create table salt

(sodium chloride) – 2Na(s) + Cl2(g) 2NaCl(s)

Decomposition Reaction

• When a single compound breaks down into 2 or more elements or compounds.

• AB A + B• Example:– Sodium azide decomposes into sodium and

nitrogen gas when an airbag inflates.– 2NaN3(s) 2Na(s) + 3N2(g)

Combustion Reaction

• When a hydrocarbon burns in oxygen to produce carbon dioxide, water, and heat. – CxHy + O2 H2O + CO2

• Also known as burning. • Example:– Methane (hydrocarbon found in natural gas) burns in

the presence of oxygen

– CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

Single Replacement Reaction• One element replaces another element in a compound. • Can be:

– Metal replaces hydrogen– metal replaces metal– Non-metal replaces non-metal

• More active elements replace less active elements.• A + BX AX + B• Example:

– When lithium is combined with water, lithium replaces hydrogen to be come lithium hydroxide, and hydrogen gas is released.

– 2Li(s) + 2H2O(l) 2LiOH(aq) + H2(g)

 

Double Replacement Reaction• Ions are exchanged between 2 compounds.• 3 general types:– Produces a gas– Produces a precipitate– Produces water (acid/base reaction)

• AX + BY AY + BX

• Example:• 2NaOH(aq) + CuCl2(aq) 2NaCl(aq) + Cu(OH)2(s)

(+) ions(-) ions

precipitate

Summary

• Synthesis– A + B AB

• Decomposition– AB A + B

• Combustion– CxHy + O2 H2O + CO2

• Single Replacement– A + BX AX + B

• Double Replacement– AX + BY AY + BX

Rules for Determining the Type of Reactions You Have

1. Does your reaction have oxygen as one of it's reactants and carbon dioxide and water as products? If yes, then it's a combustion reaction

2. Does your reaction have two (or more) chemicals combining to form one chemical? If yes, then it's a synthesis reaction

3. Does your reaction have one large molecule falling apart to make several small ones? If yes, then it's a decomposition reaction

4. Does your reaction have any molecules that contain only one element? If yes, then it's a single displacement reaction

5. If you haven't answered "yes" to any of the questions above, then you've got a double displacement reaction– Does this double replacement reaction have water as one of the products? If yes,

then it's an acid-base reaction– Does this double replacement reaction form a solid? If yes, it forms a precipitate.– Does this double replacement reaction form a gas? If yes, then it forms a gas. Duh.

• Determine the reaction type for each of the following equations:

1. 2Fe + O2 2FeO

2. 4Fe + 3O2 2Fe2O3

3. 2C4H10 + 13O2 8CO2 + 10H2O

4. Ca(OH)2 + H3PO4 Ca3(PO4)2 + H2O

5. 2NaCl 2Na + Cl2

6. 2Na + 2H2O 2NaOH + H2

7. N2 + 3H2 2NH3

8. HCl + FeS FeCl2 + H2S

9. Fe + CuSO4 FeSO4 + Cu

10.2P + 3Cl2 2PCl3

11.HCl + AgNO3 HNO3 + AgCl

SYNTHESISSYNTHESIS

COMBUSTIONDOUBLE DISPLACEMENT

SINGLE DISPLACEMENTDOUBLE REPLACEMENT

SYNTHESISSINGLE REPLACEMENT

DECOMPOSITION

DOUBLE DISPLACEMENTSYNTHESIS

Practice

Practice

• WS #5 Types of Rxns

Predicting Single Replacement Reactions

• A + BX AX + B• Single replacement reactions will

not occur if the metal or non metal doing the replacing is less reactive.

• For example:– 2K + MgCl2 2KCl + Mg (reacts)– Zn + NaCl NR (no reaction)

• The same happens with halogens:– F > Cl > Br > I

Warnings

• Metals ONLY replace metals or hydrogen– Metals from Li to Na will replace hydrogen in acids

AND water.– Metals from Mg to Pb will only replace hydrogen in

acids. • Halogens ONLY replace halogens• Metal + H2O H2 + metal hydroxide– NOT a metal oxide!!– Ex., Na + H2O H2 + NaOH

Replace H in acids& water

Only replace H in acids

Practice

• WS #6 Single Replacement w/ Activity Series• WS #7 Single Replacement w/ AS

Double Replacement Rxns & Solubility Rules

• AX + BY AY + BX• Double replacement reactions occur in water

(aqueous solution).• These reactions only occur if at least one of the

products is insoluble; i.e., it forms a: – gas (g) [specifically: H2S, H2CO3, H2SO3 and NH4OH]– solid precipitate (s) – water

• If both products are soluble (aq), then NO REACTION

Double Replacement Rxns & Solubility Rules Soluble = (aq) insoluble = (s)

• To determine what is soluble, you can use the following general solubility rules. They work most of the time…

• Rule 1. All compounds of Group 1 elements (the alkali metals) are soluble.• Rule 2. All ammonium salts (salts of NH4

+) are soluble.

• Rule 3. All nitrate (NO3-), chlorate (ClO3

-), perchlorate (ClO4-), and acetate (C2H3O2

-) salts are soluble.

• Rule 4. All chloride (Cl-), bromide (Br-), and iodide (I-) salts are soluble except for those of Ag+, Pb2+, and Hg22+.

• Rule 5. All sulfate ( SO4-2) compounds are soluble except those of Ba2+, Sr2+, Ca2+, Pb2+, Hg2

2+, and Hg2+, Ca2+ and Ag+ sulfates are only moderately soluble (so a precipitate will form).

• Rule 6. All hydroxide (OH-) compounds are insoluble except those of Group I-A (alkali metals) and Ba2+, Ca2+, and Sr2+.

• Rule 7. All sulfide (S2-) compounds are insoluble except those of Groups 1 and 2 (alkali metals and alkali earths).

• Rule 8. All sulfites (SO3=), carbonates (CO3

=), chromates (CrO4=), and phosphates (PO4

3-) are insoluble except for those of NH4

+ and Group 1 (alkali metals)(see rules 1 and 2).

• Rule 9. Oxides (O2-) are usually insoluble. Exceptions include Na2O, K2O, SrO, and BaO, which are soluble, and CaO, which is slightly soluble.

Double Replacement Rxns & Solubility Rules

• Determine whether or not the following compounds are soluble:– Ammonium acetate– Barium hydroxide– Zinc hydroxide– Zinc chloride– Strontium chromate– Mercury (I) sulfate– Silver bromide

Soluble #2, #3

Soluble #6

Insoluble #6

Soluble #4

Moderately Soluble = Precipitate #5

Insoluble #8

Insoluble #4

Double Replacement Rxns & Solubility Rules

• Predict whether or not the reaction will occur. If the reaction occurs, predict the products and write a balanced chemical reaction.

• Remember:– Soluble = (aq) and insoluble = (s)

• FeBr2(aq) + K2CO3(aq)

• Ag2S(aq) + CuCl2(aq)

• NaNO3(aq) + HI(aq)

Double Replacement Rxns & Solubility Rules

• Predict whether or not the reaction will occur. If the reaction occurs, predict the products and write a balanced chemical reaction.

• Remember:– Soluble = (aq) and insoluble = (s)

• FeBr2(aq) + K2CO3(aq) 2KBr(aq) + FeCO3(s)

• Ag2S(aq) + CuCl2(aq) CuS(s) + 2AgCl(s)

• NaNO3(aq) + HI(aq) NR (no precipitate)

Practice

• WS #7.1 Double Replacement Rxns &Solubility Rules

Predicting Products for all Rxns

• For predicting products in general, (1) identify the type of reaction, and then (2) apply the general rule for that reaction.

• For example, predict the following:– Ca(OH)2 + Na2CO3 ???– 2 ionic compounds = double replacement– Switch your cations using proper naming rules– Check solubility rules– Ca(OH)2(aq) + Na2CO3(aq) 2NaOH(aq) + CaCO3(s)

Both soluble At least one (s), (g), or water

Guidelines for Predicting Products• Combustion (burning)

– Hydrocarbon + oxygen carbon dioxide + water• Synthesis

– 2 elements combine one products– 2 simple compounds combine one product

• Decomposition– One reactant parts

• Single Replacement– Element + compound new compound + different element– Check activity series– Metal metal, metal hydrogen; halogen halogen

• Double Replacement– 2 ionic compounds two different ionic compounds– Switch your cations (usually metals)– Check your solubility rules: These reactions will only occur if both reactants are

soluble in water and one of the products is insoluble, a gas, or water.• Exception: Acid/base reactions produce water, and both reactants do not have to be

soluble

Predicting Decomposition Reactions – Memorize!!!

• Metallic Hydroxides Metal Oxide + H2O– Ca(OH)2(s) → CaO(s) + H2O(g)

• Metallic Carbonates Metal Oxide + CO2

– CaCO3(s) → CaO(s) + CO2(g)

• Metallic Chlorates Metal Chloride + O2

– 2KClO3 (s) → 2KCl (s) + 3O2 (g)

• Oxyacids Non-Metallic Oxide + H2O– H2SO4 (aq) → SO3 (g) + H2O (l)

Practice

• WS #8 Predicting Products• WS #9 Predicting• WS #10 Predicting

Reactions in Aqueous Solutions: Special Cases of Double-Replacement Reactions

• 3 Special Cases:– Reactions that form precipitates (solids)– Reactions that form a gas– Reactions that form water (acid/base or neutralization)

• Solute = what is dissolved• Solvent = what something is dissolved in• Aqueous solution = solvent is water• Some solutes are molecular compounds that remain as molecules in

solution.• Other solutes are molecular compounds that form ions in solution.• You must be able to write complete ionic equations and net ionic

equations (no spectator ions) for reactions that involve ions in aqueous solutions.

Reactions That Form Precipitates

• A double-displacement reaction• The molecular compounds form ions in solution• Must write complete & net ionic equations• Example:– Aqueous solutions of sodium hydroxide and

copper(II) chloride for sodium chloride and copper(II) hydroxide (the precipitate).

– 2NaOH(aq) + CuCl2(aq) 2NaCl(aq) + Cu(OH)2(s)

Net Ionic Equations• Double replacement rxns that form a precipitate should be written in the form of a net ionic equation.

For example:

• AB(aq) + CD(aq) → AD(aq) + CB(s)

• Can be written as:

• A+(aq) + B-(aq) + C+(aq) + D-(aq) → A+(aq) + D-(aq) + CB(s)

• In the equation above, A+and D- ions are present on both sides of the equation. These are called spectator ions because they remain unchanged throughout the reaction. Since they go through the equation unchanged, they can be eliminated to show the net ionic equation:

• C+ (aq)+ B- (aq) → CB (s)

• The net ionic equation only shows the precipitation reaction. A net ionic equation must be balanced on both sides not only in terms of atoms of elements but also in terms of electric charge. Precipitation reactions are usually represented solely by their net ionic equation. If all products are aqueous, a net ionic equation cannot be written because all ions are cancelled out as spectator ions. Therefore, no precipitation reaction occurs.

Ionic Equations of Precipitate Reaction

• 2NaOH(aq) + CuCl2(aq) 2NaCl(aq) + Cu(OH)2(s)Written showing all ions you get:• 2Na+(aq) + 2OH-(aq) + Cu2+(aq) + 2Cl-(aq) 2Na+(aq)

+ 2Cl-(aq) + Cu(OH)2(s)

However, removing the ions that do not participate (in reactants and products) leaves the net ionic equation:

• 2OH-(aq) + Cu2+(aq) Cu(OH)2(s)

Reactions That Form Water• Double-displacement reaction• No evidence of reaction is observable, because reaction

creates more solvent.• For example, when you mix hydrobromic acid with sodium

hydroxide, sodium bromide and water are formed. • HBr(aq) + NaOH(aq) H20(l) + NaBr(aq)• The Ionic Equation is:• H+(aq) + Br-(aq) + Na+(aq) + OH-(aq) H2O(l) + Na+(aq) + Br-(aq)• Net Ionic Equation:• H+(aq) + OH-(aq) H2O(l)

Reactions That Form Gases

• Double-displacement reaction• Hydroiodic acid and lithium sulfide react to form

hydrogen gas and lithium iodide.• 2HI(aq) + Li2S(aq) H2S(g) + 2LiI(aq)• Complete ionic equation:• 2H+(aq) + 2I-(aq) + 2Li+(aq) + S2-(aq) H2S(g) + 2Li+(aq)

+ 2I-(aq)• Net ionic equation:• 2H+(aq) + S2-(aq) H2S(g)

Another Example

• When sodium hydrogen carbonate is dissolved in hydrochloric acid, and gas producing double-displacement reaction occurs simultaneously with a decomposition reaction.

• HCl(aq) + NaHCO3(aq) H2CO3(aq) + NaCl(aq) and H2CO3(aq) H2O(l) + CO2(g)

Combining the 2 Reactions Yields• HCl(aq) + NaHCO3(aq) H2CO3(aq) + NaCl(aq)• H2CO3(aq) H2O(l) + CO2(g)

+____________________________________• HCl(aq) + NaHCO3(aq) + H2CO3(aq) H2CO3(aq) + NaCl(aq) + H2O(l) + CO2(g) • Removing substances on both sides yields: • HCl(aq) + NaHCO3(aq) NaCl(aq) + H2O(l) + CO2(g)

Complete & Net Ionic Equations

• H+(aq) + Cl-(aq) + Na+(aq) + HCO3-(aq) H2O(l)

+ CO2(g) + Na+(aq) + Cl-(aq)Removing spectator ions:• H+(aq) + Cl-(aq) + Na+(aq) + HCO3

-(aq) H2O(l) + CO2(g) + Na+(aq) + Cl-(aq)

So the net ionic equation is:• H+(aq) + HCO3

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

Practice