Chemical ReAcTiONS

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Chemical ReAcTiONS
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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 arent 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

• the arrow separates the reactants from the
  products
• Read reacts to form
• The plus sign is read 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 supplied, 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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Diatomic elements

• There are 7 elements that never want to be alone.
• They form diatomic molecules.
• H2 , N2 , O2 , F2 , Cl2 , Br2 and I2 ,
• The ogens and the ines
• 7 pattern on the periodic table

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Diatomic Elements
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Skeleton Equation

• Uses formulas and symbols to describe a reaction
• doesnt 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.
• 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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Chemical Equation

• Fe2S3(s) HCl(g) ? FeCl2(s) H2S(g)
• HNO3(aq) Na2CO3(s) ? H2O(l)
  CO2(g) NaNO3(aq)

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The other way

• Fe(g) O2(g) Fe2O3(s)
• Iron metal plus oxygen gas reacts to form Iron
  (III) Oxide rust
• This reaction is also called Corrosion
• Cu(s) AgNO3(aq) Ag(s) Cu(NO3)2(aq)
• Copper metal plus silver nitrate dissolved in
  water, reacts to form silver metal plus copper
  (II) nitrate dissolved in water.

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Balancing Chemical Equations
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Balanced Equation

• Atoms cant be created or destroyed
• All the atoms we start with we must end up with
• A balanced equation has the same number of each
  element on both sides of the equation.
• Atoms are rearranged in a chemical reaction

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O

C
C
O
O
O

• C(s) O2(g) CO2(g)
• This equation is balanced
• What if it wasnt?

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O

C
C
O
O

• If there isnt enough oxygen carbon monoxide will
  form instead!
• C(s) O2(g) CO(g)
• Now the equation isnt balanced.
• Cant change the molecular formulas

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C
C
O

O

O
C
C
O

• Can change the number of molecules
• Two carbon atoms react with one oxygen molecule
  to produce two carbon monoxide gas molecules.

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C
C
O

O

O
C
O
C

• Must have started with two C and made two CO
• 2 C O2 2 CO

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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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NEVER-NEVER-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.

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Example
H2
H2O
O2

Make a table to keep track of where you are at
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Example
H2
H2O
O2

R
P
H
2
2
O
2
1
Need twice as much O in the product
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Example
H2
H2O
O2

2
R
P
H
2
2
O
2
1
Changes the O
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Example
H2
H2O
O2

2
R
P
H
2
2
O
2
1
2
Also changes the H
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Example
H2
H2O
O2

2
R
P
H
2
2
4
O
2
1
2
Need twice as much H in the reactant
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Example
H2
H2O
O2

2
2
R
P
H
2
2
4
O
2
1
2
Recount
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Example
H2
H2O
O2

2
2
R
P
H
2
2
4
4
O
2
1
2
The equation is balanced, has the same number of
each kind of atom on both sides
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Example
H2
H2O
O2

2
2
R
P
H
2
2
4
4
O
2
1
2
This is the answer
Not this
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Examples

• CH4 O2 CO2 H2O
• AgNO3 Cu Cu(NO3)2 Ag
• Mg N2 Mg3N2
• P O2 P4O10
• Na H2O H2 NaOH

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Homework

• 14. a) Pb(NO3)2 K2CrO4 ? PbCrO4 KNO3
• b) MnO2 HCl ? MnCl2 H2O Cl2
• c) C3H6 O2 ?CO2 H2O
• d) Zn(OH)2 H3PO4 ? Zn3(PO4)2
• e) CO Fe2O3 ?Fe CO2
• f) CS2 Cl2 ?CCl4 S2Cl2
• g) CH4 Br2 ? CH3Br HBr
• h) Ba(CN)2 H2SO4 ? BaSO4 HCN

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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

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Types of Reactions

• Predicting the Products

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Types of Reactions

• There are millions of reactions.
• Cant remember them all
• Fall into several 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.
• Will recognize them by the reactants

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1 Combination Reactions

• Combine - put together
• 2 elements, or compounds combine to make one
  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
• Fe O2 iron (II) oxide
• Al O2
• Remember that the first step is to write the
  formula
• Then balance

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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
• HgO

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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
• H2CO3(aq)

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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

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3 Single Replacement

• Exceptions weve missed along the way
• Zinc, Zn, always forms a 2 ion doesnt need
  parenthesis
• ZnCl2 is zinc chloride
• Silver, Ag, always forms a 1 ion
• AgCl is silver chloride

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3 Single Replacement

• Metals replace metals (and hydrogen)
• K AlN
• Zn HCl
• 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 155
• Higher on the list replaces lower.
• If the element by itself is higher, it happens,
  in lower it doesnt

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3 Single Replacement

• Note the
• H can be replaced in acids by everything higher
• Only the first 5 (Li - Na) react with water.
• Fe CuSO4
• Pb KCl
• Al HCl

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3 Single Replacement

• What does it mean that Au And Ag are on the
  bottom of the list?
• 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

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STOP
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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- Na1Cl-1
• NaOH FeCl3 Fe(OH)3 NaCl

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4 Double Replacement

• Will only happen if one of the products
• doesnt dissolve in water and forms a solid
• or is a gas that bubbles out.
• or is a covalent compound usually water.

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Complete and balance

• assume all of the reactions take place.
• CaCl2 NaOH
• CuCl2 K2S
• KOH Fe(NO3)3
• (NH4)2SO4 BaF2

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How to recognize which type

• Look at the reactants
• E E Combination
• C Decomposition
• E C Single replacement
• C C Double replacement

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Examples

• H2 O2
• H2O
• Zn H2SO4
• HgO
• KBr Cl2
• AgNO3 NaCl
• Mg(OH)2 H2SO3

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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.

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Examples

• C4H10 O2 (complete)
• C4H10 O2 (incomplete)
• C6H12O6 O2 (complete)
• C8H8 O2 (incomplete)

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• 23. Distinguish between complete an incomplete
  combustion,.
• 24. Write a balanced equation for the complete
  combustion of each of these compounds.
• a) acetic acid, HC2H3O2 c) glycerol, C3H8O3
• b) decane, C10H22 d) sucrose, C12H22O11
• 32. Write a balanced equation for the incomplete
  combustion of each of these compounds.
• a) glycerol, C3H8O3 c) acetic acid,
  HC2H3O2
• b) glucose, C6H12O6 d) acetylene, C2H2

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Chapter 7 Summary
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An equation

• Describes a reaction
• Must be balanced because to follow Law of
  Conservation of Energy
• Can only be balanced by changing the
  coefficients.
• Has special symbols to indicate state, and if
  catalyst or energy is required.

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Reactions

• Come in 5 types.
• Can tell what type they are by the reactants.
• Single Replacement happens based on the activity
  series using activity series.
• Double Replacement happens if the product is a
  solid, water, or a gas.

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The Process

• Determine the type by looking at the reactants.
• Put the pieces next to each other
• Use charges to write the formulas
• Use coefficients to balance the equation.

Homework