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Chapter 11. Chemical Reactions. All chemical reactions. have two parts Reactants - the substances you start with Products - the substances you end up with The reactants turn into the products. Reactants ® Products. In a chemical reaction. The way atoms are joined is changed

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Chapter 11 l.jpg

Chapter 11

Chemical Reactions

All chemical reactions l.jpg
All chemical reactions

  • have two parts

  • Reactants - the substances you start with

  • Products- the substances you end up with

  • The reactants turn into the products.

  • Reactants ® Products

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In a chemical reaction

  • The way atoms are joined is changed

  • Atoms aren’t created or destroyed.

  • Can be described several ways

  • In a sentence

    • Copper reacts with chlorine to form copper (II) chloride.

  • In a word equation

  • Copper + chlorine ® copper (II) chloride

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Symbols used in equations

  • Table 11.1

  • the arrow separates the reactants from the products

  • Read “reacts to form”

  • The plus sign = “and”

  • (s) after the formula -solid

  • (g) after the formula -gas

  • (l) after the formula -liquid

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Symbols used in equations

  • (aq) after the formula - dissolved in water, an aqueous solution.

  • ­ used after a product indicates a gas (same as (g))

  • ¯ used after a product indicates a solid (same as (s))

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Symbols used in equations

  • indicates a reversible reaction (More later)

  • shows that heat is supplied to the reaction

  • is used to indicate a catalyst used in this case, platinum.

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What is a catalyst?

  • A substance that speeds up a reaction without being changed by the reaction.

  • Enzymes are biological or protein catalysts.

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Skeleton Equation

  • Uses formulas and symbols to describe a reaction

  • doesn’t indicate how many.

  • All chemical equations are sentences that describe reactions.

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Convert these to equations

  • Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form solid iron (II) chloride and hydrogen sulfide gas.

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Convert these to equations

  • Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.

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The other way

  • Fe(g) + O2(g) ® Fe2O3(s)

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The other way

  • Cu(s) + AgNO3(aq) ® Ag(s) + Cu(NO3)2(aq)

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Balanced Equation

  • Atoms can’t be created or destroyed

  • All the atoms we start with we must end up with

  • A balanced equation has the same number of atoms of each element on both sides of the equation.

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  • C + O2® CO2

  • This equation is already balanced

  • What if it isn’t already?






Slide16 l.jpg











  • C + O2® CO

  • We need one more oxygen in the products.

  • Can’t change the formula, because it describes what actually happens

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  • Must have started with two C

  • 2 C + O2® 2 CO


  • Must be used to make another CO

  • But where did the other C come from?

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Rules for balancing

  • Write the correct formulas for all the reactants and products

  • Count the number of atoms of each type appearing on both sides

  • Balance the elements one at a time by adding coefficients (the numbers in front)

  • Check to make sure it is balanced.

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  • Change a subscript to balance an equation.

    • If you change the formula you are describing a different reaction.

    • H2O is a different compound than H2O2

  • Never put a coefficient in the middle of a formula

    • 2 NaCl is okay, Na2Cl is not.

Example l.jpg

H2 +

H2 +





















Need twice as much H in the reactant


Need twice as much O in the product

Changes the O

Make a table to keep track of where you

are at

Also changes the H

The equation is balanced, has the same

number of each kind of atom on both sides

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This is the answer

Not this



H2 +
















Examples l.jpg

CH4 + O2® CO2 + H2O

Examples23 l.jpg

AgNO3 + Cu ® Cu(NO3)2 + Ag

Examples24 l.jpg

Al + N2® Al2N3

Examples25 l.jpg

P + O2® P4O10

Examples26 l.jpg

Na + H2O ® H2 + NaOH

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  • If an atom appears more than once on a side, balance it last.

  • If you fix everything except one element, and it is even on one side and odd on the other, double the first number, then move on from there.

  • C4H10 + O2 CO2 + H2O

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Types of Reactions

Predicting the Products

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Types of Reactions

  • There are too many reactions to remember

  • Fall into categories.

  • We will learn 5 types.

  • Will be able to predict the products.

  • For some we will be able to predict whether they will happen at all.

  • Must recognize them by the reactants

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#1 Combination Reactions

  • Combine - put together

  • 2 elements, or compounds combine to make 1 compound.

  • Ca +O2® CaO

  • SO3 + H2O ® H2SO4

  • We can predict the products if they are two elements.

  • Mg + N2®

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Write and balance

  • Ca + Cl2®

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Write and balance

  • Fe + O2® iron (II) oxide

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Write and balance

  • Al + O2®

  • Remember that the first step is to write the formula

  • Then balance

  • Also called synthesis reaction

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Combining two compounds

  • If they tell you it is combination, you will make one product

  • Two compounds will make a polyatomic ion.

  • CO2 + H2O →

  • H2O + Cl2O7→

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#2 Decomposition Reactions

  • decompose = fall apart

  • one reactant falls apart into two or more elements or compounds.

  • NaCl Na + Cl2

  • CaCO3 CaO + CO2

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#2 Decomposition Reactions

  • Can predict the products if it is a binary compound

  • Made up of only two elements

  • Falls apart into its elements

  • H2O

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#2 Decomposition Reactions

  • If the compound has more than two elements you must be given one of the products

  • The other product will be from the missing pieces

  • NiCO3 NiO +

  • H2CO3(aq)® CO2 +

3 single replacement l.jpg
#3 Single Replacement

  • One element replaces another

  • Reactants must be an element and a compound.

  • Products will be a different element and a different compound.

  • Na + KCl ® K + NaCl

  • F2 + LiCl ® LiF + Cl2

Na kcl k nacl l.jpg
Na + KCl ® K + NaCl




F 2 2 licl 2 lif cl 2 l.jpg
F2 + 2 LiCl ® 2 LiF + Cl2









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#3 Single Replacement

  • Metals replace metals (and hydrogen)

  • Al + CuSO4®

  • Zn + H2SO4®

  • Think of water as HOH

  • Metals replace one of the H, combine with hydroxide.

  • Na + HOH ®

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#3 Single Replacement

  • We can tell whether a reaction will happen

  • Some are more active than other

  • More active replaces less active

  • There is a list on page 333

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#3 Single Replacement

  • There is a list on page 333

  • Higher on the list replaces lower.

  • If the element by itself is higher, it happens,

  • if element by itself is lower, it doesn’t

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#3 Single Replacement

  • Note the *

  • H can be replaced in acids by everything higher

  • Only the first 4 (Li - Na) react with water.

3 single replacement47 l.jpg
#3 Single Replacement

  • Fe + CuSO4®

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#3 Single Replacement

  • What does it mean that Ag is on the bottom of the list?

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#3 Single Replacement

  • Nonmetals can replace other nonmetals

  • Limited to F2 , Cl2 , Br2 , I2

  • The order of activity is that on the table.

  • Higher replaces lower.

  • F2 + HCl ®

  • Br2 + KCl ®

4 double replacement l.jpg
#4 Double Replacement

  • Two things replace each other.

  • Reactants must be two ionic compounds or acids.

  • Usually in aqueous solution

  • NaOH + FeCl3®

  • The positive ions change place.

  • NaOH + FeCl3® Fe3+OH- + Na+Cl-

  • NaOH + FeCl3® Fe(OH)3 + NaCl

3naoh fecl 3 fe oh 3 3nacl l.jpg







3NaOH + FeCl3® Fe(OH)3 + 3NaCl








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#4 Double Replacement

  • Will only happen if one of the products

    • doesn’t dissolve in water and forms a solid

    • or is a gas that bubbles out.

    • or is a covalent compound usually water.

  • Polyatomic ions don’t change from side to side

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Complete and balance

  • assume all of the reactions take place.

  • CaCl2 + NaOH ®

  • CuCl2 + K2S ®

  • KOH + Fe(NO3)3®

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Complete and balance

  • KOH + Fe(NO3)3®

  • H3PO4 + Ca(OH)2®

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How to recognize which type

  • Look at the reactants

  • E for element

  • C for compound

  • E + E Combination

  • C Decomposition

  • E + C Single replacement

  • C + C Double replacement

Last type l.jpg
Last Type

  • Combustion

  • A compound composed of only C H and maybe O is reacted with oxygen

  • If the combustion is complete, the products will be CO2 and H2O.

  • If the combustion is incomplete, the products will be CO and H2O.

  • or just C and H2O.

  • O2 will always be the second reactant

Examples59 l.jpg

  • Complete combustion of C4H10

  • Incomplete combustion of C4H10

Examples60 l.jpg

  • Complete combustion of C6H12O6

  • Incomplete combustion of C2H6O

Ionic compounds and acids l.jpg
Ionic Compounds and acids

  • Fall apart into ions when they dissolve

  • That’s why they conduct electricity when dissolved.

  • So when we write them as (aq) they are really separated

  • NaCl(aq) is really Na+(aq) and Cl-(aq)

  • K2SO4 (aq) is really K+(aq) and SO42-(aq)

Reactions in aqueous solutions l.jpg
Reactions in aqueous solutions

  • Many reactions happen in solution

  • Makes it so the ions separate so they can interact.

  • Solids, liquids, and gases are not separated, only aqueous

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Complete Ionic Equation

  • Every aqueous compound is written as separate ions

  • Solids, liquids and gases as whole compounds

  • MgCl2(aq) + PbSO4(aq) → MgSO4(aq) + PbCl2(s)

  • Is really

  • Mg2+(aq) + Cl-(aq) + Pb2+(aq) + SO4(aq) →Mg2+(aq) + SO4(aq) + PbCl2(s)

Write the complete ionic equation for l.jpg
Write the complete ionic equation for

  • FeBr3(aq) + KOH(aq) → KBr(aq) + Fe(OH)3(s)













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Write the complete ionic equation for

  • CaCl2(aq) + MgSO4(aq) → CaSO4(s) + MgCl2(aq)

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Write the complete ionic equation for

  • Ba(OH)2(aq) + H2SO4(aq) → BaSO4(s) + HOH(l)

The complete ionic equation is l.jpg
The complete ionic equation is

  • Fe3+(aq)+ Br-(aq) + K+(aq) +OH-(aq) →K+(aq) +Br-(aq) + Fe(OH)3(s)

  • K+ and Br- don’t change.

  • They are spectator ions

  • Could be eliminated

  • Fe3+(aq) +OH-(aq) →Fe(OH)3(s)

  • This is what really changes

Net ionic equation l.jpg
Net ionic equation

  • Shows only those particles that change before and after.

  • Eliminate spectator ions

  • Needs to be balanced in terms of both mass and charge

  • Fe3+(aq) +OH-(aq) →Fe(OH)3(s)

  • Fe3+(aq) +3 OH-(aq) →Fe(OH)3(s)

Write the net ionic equation l.jpg
Write the net ionic equation

  • HCl (aq) + Ba(OH)2 (aq) → BaCl2(s) + HOH (l)

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Write the net ionic equation

  • Al + FeSO4(aq)→ Al2(SO4)3(aq) + Fe

Write the net ionic equation71 l.jpg
Write the net ionic equation

  • Cl2(s) + NaI(aq)→ NaCl(aq) + I2(s)

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Write the net ionic equation

  • K2CO3(aq) + MgI2(aq) → MgCO3(s) + KI(aq)

Net ionic equations l.jpg
Net ionic equations

  • Written for single and double replacement.

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Predicting precipitates

  • Solids formed from aqueous solution.

  • You can predict them if you know some general rules for solubility.

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These things are soluble

  • Salts with alkali metals and ammonium

  • Salts of nitrates and chlorates

  • Salts of sulfates except Ag+, Pb2+, Hg22+, Ba2+, and Sr2+

  • Salts of chlorides except Ag+, Pb2+, and Hg22+

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These things are insoluble

  • Carbonates, phosphates, chromates, sulfides, and hydroxides

  • Unless they fall under rule # 1

Is it soluble l.jpg
Is it soluble?

  • LiBr

  • Ba(NO3)2

  • CaSO4

  • PbCl2

  • CaCO3

  • K2CO3

  • Cd(ClO3)2

Is there a reaction l.jpg
Is there a reaction?

  • For double replacement- has to make gas, solid or water.

  • Water from an acid- H+ and a hydroxide- OH- makes HOH

  • Solids- from solubility rules

  • Exchange ions and see if something is insoluble

Is there a reaction79 l.jpg
Is there a reaction?

  • MgSO4 + NaOH →

  • H2SO4 + KOH →

  • K3PO4 + FeF3→

An equation l.jpg
An equation

  • Describes a reaction

  • Must be balanced to follow the

    Law of Conservation of Mass

  • Can only be balanced by changing

    the coefficients.

  • Has special symbols to indicate state, and if catalyst or energy is required.

Reactions l.jpg

  • Come in 5 types.

  • Can tell what type they are by the reactants.

  • Single Replacement happens based on the activity series

  • Double Replacement happens if the product is a solid, water, or a gas.

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The Process

1. Determine the type by looking at the reactants.

2. Put the pieces next to each other based on type

3. Use charges to write the formulas

  • Elements get 2?

    4. Use coefficients to balance the equation.