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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


In a chemical reaction l.jpg
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 l.jpg
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 l.jpg
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)


The other way12 l.jpg
The other way

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



Balanced equation l.jpg
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 l.jpg

®

O

+

  • C + O2® CO2

  • This equation is already balanced

  • What if it isn’t already?

C

C

O

O

O


Slide16 l.jpg

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 l.jpg

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?


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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

  • 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 +

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 l.jpg

This is the answer

Not this

Example

2

H2 +

O2

®

2

H2O

R

P

4

2

H

2

4

2

O

1

2


Examples l.jpg
Examples

CH4 + O2® CO2 + H2O


Examples23 l.jpg
Examples

AgNO3 + Cu ® Cu(NO3)2 + Ag


Examples24 l.jpg
Examples

Al + N2® Al2N3


Examples25 l.jpg
Examples

P + O2® P4O10


Examples26 l.jpg
Examples

Na + H2O ® H2 + NaOH


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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


Types of reactions l.jpg

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


1 combination reactions l.jpg
#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®


Write and balance32 l.jpg
Write and balance

  • Fe + O2® iron (II) oxide


Write and balance33 l.jpg
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→


2 decomposition reactions l.jpg
#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 l.jpg
#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

Cl

K

Na


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

Cl

Li

Li

F

F

Cl

Li

Li


3 single replacement42 l.jpg
#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 l.jpg
#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 l.jpg
#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 l.jpg
#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®




3 single replacement50 l.jpg
#3 Single Replacement

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


3 single replacement51 l.jpg
#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

O-

O-

O-

H+

H+

H+

3NaOH + FeCl3® Fe(OH)3 + 3NaCl

Na+

Cl-

Cl-

Fe3+

Na+

Cl-

Na+


4 double replacement54 l.jpg
#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 l.jpg
Complete and balance

  • assume all of the reactions take place.

  • CaCl2 + NaOH ®

  • CuCl2 + K2S ®

  • KOH + Fe(NO3)3®


Complete and balance56 l.jpg
Complete and balance

  • KOH + Fe(NO3)3®

  • H3PO4 + Ca(OH)2®


How to recognize which type l.jpg
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
Examples

  • Complete combustion of C4H10

  • Incomplete combustion of C4H10


Examples60 l.jpg
Examples

  • 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


Complete ionic equation l.jpg
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)

Fe3+(aq)

Br-(aq)

K+(aq)

OH-(aq)

K+(aq)

Br-(aq)

Fe(OH)3(s)

+

+

+

+

+


Write the complete ionic equation for65 l.jpg
Write the complete ionic equation for

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


Write the complete ionic equation for66 l.jpg
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)


Write the net ionic equation70 l.jpg
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)


Write the net ionic equation72 l.jpg
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.


Predicting precipitates l.jpg
Predicting precipitates

  • Solids formed from aqueous solution.

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


These things are soluble l.jpg
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 l.jpg
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
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 l.jpg
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.