Chapter 10
Reactions & Equations
 Chemical Reaction
 Process where the atoms of 1 or more substances are
rearranged to form different substances
 Evidence for chemical rxns
 Temp. change
 Color change
 Odor
 Gas bubbles
 Change in other appearance
Reactions & Equations
 Use chemical equations to represent rxns
 Reactants: Starting substances
 Products: Substances formed during the rxn
 Chemical eq. show direction of rxn
 Reactant 1 + Reactant 2 -> Product 1 + Product 2
 Symbols are used to show physical states
 g = gas, s = solid, l = liquid, aq = aqueous (something
dissolved in water)
Reactions & Equations
 Word Equations
 Iron (s) + chlorine (g) -> iron (III) chloride (s)

Iron and chlorine react to form iron (III) chloride
 Skeleton Equations
 Uses chemical formulas
 Fe (s) + Cl2 (s) -> FeCl3 (s)
 Write the skeleton eq for the rxn between carbon & sulfur to
form carbon disulfide
 Write the chemical formula for reactants
 Write the chemical formula for products

C (s) + S (s) -> CS2 (l)
Practice Probs
 Write the skeleton equations for the following:
 Hydrogen (g) + Bromine (g) -> Hydrobromic acid (g)
 H2 (g) + Br2 (g) -> HBr (g)
 Carbon monoxide (g) + Oxygen (g) -> Carbon dioxide
 CO (g) + O2 (g) -> CO2
Reactions & Equations
 Balancing Chemical Equations
 Chemical eq must show the conservation of mass (in this case
atoms)
 For example:
 2Fe (s) + 3Cl2 (g) -> 2FeCl3 (s)


2 Fe atoms on each side
6 Cl atoms on each side
 The #’s in front of reactant/product is called a coefficient
(the # written in front of a reactant or product)
 Reactants/products w/out a coefficient have a coefficient of 1
Reactions & Equations
 Balance: Hydrogen and chlorine react to form hydrochloric acid
 Steps for Balancing Equations:
 Write the skeleton equation

H2 (g) + Cl2 (g) -> HCl (g)
 Count the atoms of the elements in reactants & products
 Reactants: 2 H
2 Cl
 Products: 1 H
1 Cl
 Change the coefficients to make the # atoms on each side equal (guess & check)
 H2 (g) + Cl2 (g) -> 2HCl (g)
 Write the coefficients in their lowest possible ratio (simplify if possible)
 Simplified
 CHECK YOUR WORK!
Practice Probs
 Write balanced chemical equations:
 Iron (III) chloride reacts w/sodium hydroxide,
producing solid iron (III) hydroxide and sodium
chloride
Practice Probs
 Write balanced chemical equations:
 Liquid carbon disulfide reacts w/oxygen gas,
producing carbon dioxide gas and sulfur dioxide gas
Practice Probs
 Write balanced chemical equations:
 Solid zinc and aqueous hydrogen sulfate react to
produce hydrogen gas and aqueous zinc sulfate
HOMEWORK
 Pg. 283 #7-13
 Pg. 304 # 71-78
Classifying Chemical Reactions
 Synthesis Reactions
 A chemical rxn where 2 or more substances react to produce a
single reaction


A + B = AB
Fe (s) + Cl2 (g)  FeCl3
 Sodium and chlorine react to produce sodium chloride
 Calcium oxide and water combine to form calcium hydroxide
 Sulfur dioxide gas reacts w/oxygen gas to form sulfur trioxide
Classifying Chemical Reactions
 Combustion Reactions
 Oxygen combines w/a substance & releases energy (heat
& light)
 Hydrogen & oxygen gas is heated to form water
 Rxn between solid carbon & oxygen gas to form carbon
dioxide & water
 Methane gas reacts w/ oxygen gas to form carbon
dioxide & water
Practice Prob 4
 The solids aluminum and sulfur react to produce
aluminum sulfide
Practice Prob 5
 Water and dinitrogen pentoxide gas react to produce
aqueous hydrogen nitrate
Practice Prob 6
 The gases nitrogen dioxide and oxygen react to
produce dinitrogen pentoxide gas.
Practice Prob 7
 Ethane gas (C2H6) burns in air producing carbon
dioxide and water vapor.
Classifying Chemical Reactions
 Decomposition Reactions
 Single compound breaks down into 2 or more
substances

AB  A + B
 Ammonium nitrate breaks down into dinitrogen
monoxide & water
 Sodium azide (NaN3) breaks down into sodium solid &
nitrogen gas. (Air bags)
Practice Prob 8
 Aluminum oxide (s) decomposes when electricity is
passed through it.
Practice Prob 9
 Nickel (II) hydroxide (s) decomposes to produce nickel
(II) oxide (s) and water.
Classifying Chemical Reactions
 Single-Replacement Reactions
 Atoms of 1 element replace the atoms of another
element in a compound

A + BX  AX + B
 Lithium (s) and water (l) react to form lithium
hydroxide (aq) and hydrogen (g)
 Copper (s) and silver nitrate (aq) react to form silver (s)
and copper nitrate (aq)
Practice Prob 10
 Predict if the following single-replacement rxn will
occur:
 K (s) + ZnCl2 (aq) 
Practice Prob 11
 Predict if the following single-replacement rxn will
occur:
 Cl2 (g) + HF (aq) 
Practice Prob 12
 Predict if the following single-replacement rxn will
occur:
 Fe (s) + Na3PO4 (aq) 
Classifying Chemical Reactions
 Double-Replacement Reactions:
 Exchange of ions between 2 compounds

AX + BY  AY + BX
 Ca(OH)2 (aq) + 2HCl (aq)  CaCl2 (aq) + 2H2O (l)
 NaOH (aq) + CuCl2 (aq)  NaCl (aq) + Cu(OH)2 (s)

Solid produced during a rxn is a precipitate
Classifying Chemical Reactions
 Double-Replacement Reactions:
 All produce either a precipitate, a gas, or water
 KCN (aq) + HBr (aq) 
Practice Prob 13
 Aqueous lithium iodide and aqueous silver nitrate
react to produce solid silver iodide and aqueous
lithium nitrate
Practice Prob 14
 Aqueous barium chloride and aqueous potassium
carbonate react to produce solid barium carbonate and
aqueous potassium chloride
HOMEWORK
 Pg. 291 # 27-32
Aqueous Solutions
 Solution contains 1 or more substances known as solutes
dissolved in another substance
 Substance that does the dissolving the solvent
 Aqueous Solution
 Solvent is water
 Many different solutes


HCl (g)  H+ (aq) + Cl- (aq)
NaOH (aq)  Na+ (aq) + OH- (aq)
 Ions in the solution may react w/other ions in solution

Double-replacement reaction
Aqueous Solutions
 Reactions that form precipitates
 2NaOH (aq) + CuCl2 (aq)  2NaCl (aq) + CuOH (s)

Double-replacement rxn
 Complete Ionic Equation

2 Na+ (aq) + 2OH- (aq) + Cu2+ (aq) + 2Cl- (aq)  2Na+ (aq) + 2Cl- (aq) + Cu(OH)2 (s)
Aqueous means they are in solution of water & are present as
ions
 Spectator Ions: Ions that do not participate in the rxn & are
found in both the reactants & products
 Na+ & Cl Net Ionic Equations: eliminate spectator ions


2OH- (aq) + Cu2+ (aq)  Cu(OH)2 (s)
Practice Prob 15
 Write the chemical, complete ionic, and net ionic
equations:
 Aqueous solutions of potassium iodide & silver nitrate
are mixed forming the precipitate silver iodide.
Practice Prob 16
 Write the chemical, complete ionic, and net ionic
equations:
 Aqueous solutions of ammonium phosphate & sodium
sulfate are mixed. No precipitate forms and no gas is
produced.
Practice Prob 17
 Write the chemical, complete ionic, and net ionic
equations:
 Aqueous solutions of aluminum chloride and sodium
hydroxide are mixed, forming the precipitate aluminum
hydroxide.
Reactions that Form Water
 Since water is formed, you cannot tell if a rxn has
occurred
 HBr (aq) + NaOH (aq)  H2) (l) + NaBr (aq)
 Reactants & product remain in solution
 Complete ionic equation:
 H+ (aq) + Br- (aq) + Na+ (aq) + OH- (aq)  H2O (l) + Na+ (aq) + Br- (aq)

Reacting ions are H+ & OH-
 Net Ionic Equation:
 H+ (aq) + OH- (aq)  H2O (l)
Practice Prob 18
 Write Chemical, Complete Ionic, & Net Ionic
equations:
 Sulfuric acid (H2SO4) & aqueous potassium hydroxide
Practice Prob 19
 Write Chemical, Complete Ionic, & Net Ionic
equations:
 Hydrochloric acid (HCl) & aqueous calcium hydroxide
Reactions That Form Gases
 Some double-replacement rxns form gases
 Carbon dioxide, hydrogen cyanide, hydrogen sulfide, & hydrogen
are common
 Chemical Equation:
 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:
 2H+ (aq) + S2- (aq)  H2S (g)
HOMEWORK
 Pg. 294 # 36-37;
 Pg. 296 # 40-42;
 Pg. 299 # 43-51