Chemical ReactionsChapter 9

Chapter ObjectivesWriting Chemical EquationsBalancing Chemical EquationsReactions in Aqueous Solutions

Predicting if a reaction will occurClassifying chemical reactions

The process by which one or more substances are rearranged to form different substances is called a chemical reaction.

Chemical ReactionsClues that a reaction has occurredWriting Chemical EquationsBalancing Chemical Equations

THINGS TO LOOK FOR IN A CHEMICAL

CHANGE1. Evolution of a gas

a. Formation of bubbles b. A distinct odor

2. Formation of a precipitate, a water insoluble product

3. Large amounts of energy released or absorbed4. A color change

Chemists use statements called equations to represent chemical reactions.

Reactants are the starting substances.Products are the substances formed in the

reaction.

Writing Chemical Equations

1.The identities of the reactants and products must be known.

2.The correct formulas of both reactants and products must be expressed.

3. The physical state of the substances may be specified for clarity.

Indicating Physical StatesGas (g)Liquid (l)Solid (s)Water solution (aq)

In word equations, aluminum(s) + bromine(l) → aluminum bromide(s)

reads as “solid aluminum and liquid bromine react to produce solid aluminum bromide”.

Skeleton equations use symbols and formulas to represent the reactants and products.

Al(s) + Br(l) → AlBr3(s)Skeleton equations lack information about how

many atoms are involved in the reaction.

A chemical equation is a statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction

Balancing Chemical Equations

A coefficient in a chemical equation is the number written in front of a reactant or product, describing the lowest whole-number ratio of the amounts of all the reactants and products.

Writing balanced equations:

Methane burns in oxygen to produce carbon dioxide and water.CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O

Solid sodium reacts with liquid water to produce hydrogen gas and dissolved sodium hydroxide (NaOH).2 Na (s) + H2 (g) 2 NaOH (aq)

Molten potassium chlorate decomposes to form gaseous oxygen and solid potassium chloride.2 KClO3 (l) 3 O2 (g) + 2 KCl (s)

In water solution, hydrochloric acid and sodium carbonate react to produce sodium chloride, water, and carbon dioxide.2 HCl (aq) + Na2CO3 (aq) 2 NaCl (aq) + H2O (l) + CO2 (g)

White phosphorus burns vigorously in air to yield diphosphorus pentaoxide. P4 (s) + 5 O2 (g) 2 P2O5 (s)

Diphosphorus pentaoxide reacts vigorously in water yielding phosphoric acid.

P2O5 (s) + 3 H2O (l) 2 H3PO4 (aq)

Magnesium reacts with air to form both magnesium oxide and magnesium nitride.

A. What is the balanced reaction forming magnesium oxide?

2 Mg (s) + O2 (g) 2 MgO (s) B. What is the balanced reaction forming

magnesium nitride?3 Mg (s) + N2 (g) Mg3N2 (s)

Magnesium nitride reacts with water forming magnesium oxide and ammonia.

Mg3N2 (s) + 3 H2O (g) 3 MgO (s) + 2 NH3 (aq)

Butane, C4H10, reacts in air to give carbon dioxide and water.

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

Types of Chemical Reactions

A + B C C A + B A + BC AC + BAB + CD AD + CBSubstance X + O2 Products

A + B C

Composition or Synthesis Reactions

H2(g) + O2(g) H2O(l)NH3(g) + H3PO4(aq)(NH4)3PO4(aq)P4(s) + S8(s) P2S5(s)

A synthesis reaction is a reaction in which two or more substances react to produce a single product.

Calcium oxide and water react to form calcium hydroxide. CaO (s) + H2O Ca(OH)2 (aq)

Sulfur dioxide reacts with oxygen to form sulfur trioxide.2 SO2 (g) + O2 (g) 2 SO3 (g)

A decomposition reaction is one in which a single compound breaks down into two or more elements or new compounds.

Decomposition reactions often require an energy source, such as heat, light, or electricity, to occur.

C A + BDecomposition ReactionsKClO3(s) KCl(s) + O2(g)

C12H22O11(s) C(s) + H2O(l)

Ammonium nitrate breaks down into dinitrogen monoxide and water when heated to a high temperature. NH4(NO3) (s) N2O (g) + 2 H2O

Sodium azide (used in air bags) decomposes producing nitrogen gas and solid sodium. (The nitrogen gas inflates the air bag.)2 NaN3 (s) 3 N2 + 2 Na (s)

In a combustion reaction, oxygen combines with a substance and releases energy in the form of heat and light.

Heated hydrogen reacts with oxygen to produce heat and water in a combustion reaction. (This is also a synthesis reaction.)2 H2 (g) + O2 (g) 2 H2O

Substance X + O2(g) Products

H2S(g) + O2(g) SO2(g) + H2O(g)

C6H14(l) + O2(g) CO2(g) + H2O(l)

C25H52(s) + O2(g) CO2(g) + H2O(l)

S8(s) + O2(g) SO2(g)

C26H20O10(s) + O2(g)CO2(g) + H2O(g)

A reaction in which the atoms of one element replace the atoms of another element in a compound is called a single replacement reaction.

A + BX → AX + B

Single Replacement Reactions

Type 1: A metal replaces hydrogen:Lithium metal reacts with water to form lithium

hydroxide and hydrogen.Type 2: A metal replaces another metal:A copper bar reacts with silver nitrate to form

silver metal and copper (II) nitrate.

A metal will not always replace a metal in a compound dissolved in water because of differing reactivities.

An activity series can be used to predict if reactions will occur.

Suppose you placed silver wire in aqueous copper(II) nitrate. Will the silver atoms replace the copper atoms?No

Type 3 Nonmetals replace nonmetals:Fluorine reacts with aqueous sodium bromide to

form aqueous sodium fluoride and liquid bromine.

Will bromine gas react with aqueous sodium fluoride to form aqueous sodium bromide?No

Double replacement reactions occur when ions exchange between two compounds.

The solid product produced during a chemical reaction in a solution is called a precipitate.

All double replacement reactions produce either water, a precipitate, or a gas.

Sodium chloride reacts with aqueous silver nitrate to form aqueous sodium nitrate and solid silver chloride.NaCl (s) + AgNO3 (aq) NaNO3 (aq) + AgCl (s)

Calcium chloride reacts with aqueous aluminum sulfate to produce solid calcium sulfate and aqueous aluminum chloride.3 CaCl2 (s) + Al2(SO4)3 (aq) 3 CaSO4 (s) +

2 AlCl3 (aq)

Reactions in Aqueous Solutions

An aqueous solution contains one or more dissolved substances (called solutes) in water.

The solvent is the most plentiful substance in a solution.

Ionic compounds can also be solutes in aqueous solutions.

When ionic compounds dissolve in water, their ions separate in a process called dissociation.

When Ionic Compounds Dissolve

NaCl in water

NaCl H2O Na+(aq) + Cl–(aq)

When two solutions that contain ions as solutes are combined, the ions might react.

If they react, it is always a double replacement reaction.

Three products can form: precipitates, water, or gases.

Aqueous solutions of sodium hydroxide and copper(II) chloride react to form the precipitate copper(II) hydroxide.

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

Ionic equations that show all of the particles in a solution as they actually exist are called complete ionic equations.

2Na+(aq) + 2OH–(aq) + Cu2+ (aq)+ 2Cl–(aq) → 2Na+(aq) + 2Cl–(aq) + Cu(OH)2(s)

Ions that do not participate in a reaction are called spectator ions and are not usually written in ionic equations.

2 Na+ + 2 OH- + Cu2+ + 2 Cl- → 2 Na+ + 2 Cl- + Cu(OH)2

Formulas that include only the particles that participate in reactions are called net ionic equations.

2 OH- + Cu2+ → Cu(OH)2

Ionic ReactionsMolecular EquationComplete Ionic EquationNet Ionic Equation

Ionic ReactionsMolecular Equation

K2SO4 + Ba(NO3)2 KNO3 + BaSO4

Ionic ReactionsComplete Ionic Equation2K+

(aq) + SO42-

(aq) + Ba2+(aq) + 2NO3

–(aq)

2K+(aq) + 2NO3

–(aq) + BaSO4 (s)

K+(aq) and NO3

–(aq) are called

spectator ions.

Ionic ReactionsNet Ionic Equation

SO42-

(aq) + Ba2+(aq) BaSO4 (s)

Ionic ReactionsMolecular EquationKCl + AgNO3 KNO3 + AgCl

Ionic ReactionsComplete Ionic EquationK+

(aq) + Cl–(aq) + Ag+(aq) + NO3

– K+

(aq) + NO3– + AgCl (s)

Ionic ReactionsNet Ionic Equation

Ag+(aq) + Cl–(aq) AgCl (s)

Write the NET ionic equation

Na2SO4 (aq) and Pb(NO3)2 (aq) SO4

2- (aq) + Pb2+(aq) PbSO4 (s)

KNO3 (aq) and BaCl2 (aq) No net reaction

KOH (aq) and Fe(NO3)3 (aq)Fe3+ (aq) + 3 OH- (aq) Fe(OH)3 (s)

Compounds

Solubility Exceptions

1 Salts of alkali metals and ammonia

Soluble Some lithium compounds

2 Nitrate salts and chlorate salts

Soluble Few exceptions

3 Sulfate salts

Soluble Compounds of Pb, Ag, Hg, Ba; Sr, and Ca

4. Chloride salts Soluble Compounds of Ag and some compounds of Hg and Pb

5 Carbonates, phosphates, chromates, sulfides, and hydroxides

Most are insoluble Compounds of the alkali metals and of ammonia