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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

Chapter 11

Chemical Reactions

all 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
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
symbols used in equations
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
symbols used in equations5
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))
symbols used in equations6
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.
what is a catalyst
What is a catalyst?
  • A substance that speeds up a reaction without being changed by the reaction.
  • Enzymes are biological or protein catalysts.
skeleton equation
Skeleton Equation
  • Uses formulas and symbols to describe a reaction
  • doesn’t indicate how many.
  • All chemical equations are sentences that describe reactions.
convert these to equations
Convert these to equations
  • Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form solid iron (II) chloride and hydrogen sulfide gas.
convert these to equations10
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.
the other way
The other way
  • Fe(g) + O2(g) ® Fe2O3(s)
the other way12
The other way
  • Cu(s) + AgNO3(aq) ® Ag(s) + Cu(NO3)2(aq)
balanced equation
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.
slide15

®

O

+

  • C + O2® CO2
  • This equation is already balanced
  • What if it isn’t already?

C

C

O

O

O

slide16

C

C

C

C

O

O

O

O

®

+

  • C + O2® CO
  • We need one more oxygen in the products.
  • Can’t change the formula, because it describes what actually happens
slide17

C

C

C

C

O

O

®

O

+

  • Must have started with two C
  • 2 C + O2® 2 CO

O

  • Must be used to make another CO
  • But where did the other C come from?
rules for balancing
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.
never
Never
  • 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

H2 +

H2 +

O2

O2

®

®

H2O

2

H2O

R

P

4

2

H

2

4

2

O

1

2

Example

2

Need twice as much H in the reactant

Recount

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

slide21

This is the answer

Not this

Example

2

H2 +

O2

®

2

H2O

R

P

4

2

H

2

4

2

O

1

2

examples
Examples

CH4 + O2® CO2 + H2O

examples23
Examples

AgNO3 + Cu ® Cu(NO3)2 + Ag

examples24
Examples

Al + N2® Al2N3

examples25
Examples

P + O2® P4O10

examples26
Examples

Na + H2O ® H2 + NaOH

techniques
Techniques
  • 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
types of reactions

Types of Reactions

Predicting the Products

types of reactions29
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
1 combination reactions
#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®
write and balance32
Write and balance
  • Fe + O2® iron (II) oxide
write and balance33
Write and balance
  • Al + O2®
  • Remember that the first step is to write the formula
  • Then balance
  • Also called synthesis reaction
combining two compounds
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→
2 decomposition reactions
#2 Decomposition Reactions
  • decompose = fall apart
  • one reactant falls apart into two or more elements or compounds.
  • NaCl Na + Cl2
  • CaCO3 CaO + CO2
2 decomposition reactions36
#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
2 decomposition reactions38
#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
#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
3 single replacement42
#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 ®
3 single replacement43
#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
3 single replacement44
#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
3 single replacement45
#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 replacement50
#3 Single Replacement
  • What does it mean that Ag is on the bottom of the list?
3 single replacement51
#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
#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

O-

O-

O-

H+

H+

H+

3NaOH + FeCl3® Fe(OH)3 + 3NaCl

Na+

Cl-

Cl-

Fe3+

Na+

Cl-

Na+

4 double replacement54
#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
complete and balance
Complete and balance
  • assume all of the reactions take place.
  • CaCl2 + NaOH ®
  • CuCl2 + K2S ®
  • KOH + Fe(NO3)3®
complete and balance56
Complete and balance
  • KOH + Fe(NO3)3®
  • H3PO4 + Ca(OH)2®
how to recognize which type
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
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
Examples
  • Complete combustion of C4H10
  • Incomplete combustion of C4H10
examples60
Examples
  • Complete combustion of C6H12O6
  • Incomplete combustion of C2H6O
ionic compounds and acids
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
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
complete ionic equation
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
Write the complete ionic equation for
  • FeBr3(aq) + KOH(aq) → KBr(aq) + Fe(OH)3(s)

Fe3+(aq)

Br-(aq)

K+(aq)

OH-(aq)

K+(aq)

Br-(aq)

Fe(OH)3(s)

+

+

+

+

+

write the complete ionic equation for65
Write the complete ionic equation for
  • CaCl2(aq) + MgSO4(aq) → CaSO4(s) + MgCl2(aq)
write the complete ionic equation for66
Write the complete ionic equation for
  • Ba(OH)2(aq) + H2SO4(aq) → BaSO4(s) + HOH(l)
the complete ionic equation is
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
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
Write the net ionic equation
  • HCl (aq) + Ba(OH)2 (aq) → BaCl2(s) + HOH (l)
write the net ionic equation70
Write the net ionic equation
  • Al + FeSO4(aq)→ Al2(SO4)3(aq) + Fe
write the net ionic equation71
Write the net ionic equation
  • Cl2(s) + NaI(aq)→ NaCl(aq) + I2(s)
write the net ionic equation72
Write the net ionic equation
  • K2CO3(aq) + MgI2(aq) → MgCO3(s) + KI(aq)
net ionic equations
Net ionic equations
  • Written for single and double replacement.
predicting precipitates
Predicting precipitates
  • Solids formed from aqueous solution.
  • You can predict them if you know some general rules for solubility.
these things are soluble
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+
these things are insoluble
These things are insoluble
  • Carbonates, phosphates, chromates, sulfides, and hydroxides
  • Unless they fall under rule # 1
is it soluble
Is it soluble?
  • LiBr
  • Ba(NO3)2
  • CaSO4
  • PbCl2
  • CaCO3
  • K2CO3
  • Cd(ClO3)2
is there a reaction
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
Is there a reaction?
  • MgSO4 + NaOH →
  • H2SO4 + KOH →
  • K3PO4 + FeF3→
an equation
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
Reactions
  • 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.
the process
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.

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