Chemical Reactions - NJCTL

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Chemical Reactions

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Table of Contents: Chemical Reactions

? Chemical Equations

Click on the topic to go to that section

? Balancing Equations

? Types of Chemical Reactions

? Precipitation Reactions ? Net Ionic Equations

? Oxidation-Reduction Reactions

? Types of Oxidation-Reduction Reactions

? Acid-Base Reactions ? Identifying Reaction Types: Summary

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Chemical Equations

Chemical equations are concise representations of chemical reactions.

+

-->

+

CH4(g) + 2O2(g) --> CO2(g) + 2H2O(g)

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Chemical Equations

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Chemical Equations

The formulas of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right).

To write a word equation, write the names of the reactants to the left of the arrow separated by plus signs.

Write the names of the products to the right of the arrow, also separated by plus signs.

Reactant + Reactant

Product + Product

Slide 7 / 142 Symbols used in chemical equations

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Word Equations

When ignited, methane gas reacts with oxygen gas to produce carbon dioxide and steam.

+

+

CH4 gas

O2 gas

CO2 gas

H2O gas

This "skeleton" equation is not balanced:

CH + O 4 (g)

2 (g)

H O + CO 2 (g)

2 (g)

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2

In the reaction

CH + O # 4 (g)

2 (g)

H O + CO 2 (g)

2 (g)

the products are:

A solids

B liquids C gases D dissolved in water (aqueous) E cannot be determined F I don't know how to answer this.

answer answer

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Skeleton equations

A skeleton equation is a chemical equation that does not indicate the relative amounts of the reactants and products.

Write the formulas of the reactants to the left of the yields sign (arrow) and the formulas of the products to the right. Here is the equation for rusting: Metallic Iron reacts with oxygen in the air to produce iron (III) oxide (rust).

Iron( metal) + Oxygen ( gas) iron (III) oxide ( solid) (word equation) Fe + O2 # Fe2O3 ( skeleton /chemical equation)

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1 In the reaction

CH + O # H O + CO 4 (g)

2 (g)

2 (g)

2 (g)

the products are:

A oxygen and water B carbon dioxide and water C oxygen and methane

D methane and carbon dioxide E I don't know the answer to this.

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Word equations to Chemical equations

Solid potasium chlorate decomposes in air to produce solid potassium chloride and oxygen gas.

The word equation is:

potasium chlorate (s) --> potassium chloride (s) + oxygen (g)

The unbalanced "skeleton" equation is:

KClO3(s)

KCl + O (s)

2(g)

Slide 13 / 142 Word equations to Chemical equations

Write the word equation, then the skeleton equation Aluminum sulfate reacts with calcium chloride to produce calcium sulfate and aluminum chloride Aluminum sulfate + calcium chloride -S->licdaelcifuomr sWulfoarted+eaqluumaitniuomn chloride

Al2(SO4)3 + CaCl2 -S->lidCeaf(oSrOS4) k+eAlelCtol3n equation

Slide 14 / 142 Law of Conservation of Mass

"We may lay it down as an incontestable axiom that, in all the operations of art and nature, nothing is created; an equal amount of matter exists both before and after the experiment. Upon this principle, the whole art of performing chemical experiments depends." --Antoine Lavoisier, 1789

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Balancing Equations

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Slide 17 / 142 Balancing chemical equations

Slide 16 / 142 Balancing chemical equations

To write a balanced chemical equation, first write the skeleton equation. Then use coefficients to balance the equation so that it obeys the law of conservation of mass. This is a balanced equation for making a bicycle. The numbers are called coefficients--small whole numbers that are placed in front of the formulas in an equation in order to balance it.

Slide 18 / 142 Balancing chemical equations

CH + 4 (g)

1C 4H

2 O # 2 (g)

4 O

CO + 2 (g)

1C 2 O

2 H O 2 (g)

2 O 4H

Reactants appear on the left side of the equation.

Products appear on the right side of the equation.

The states of the reactants and products are written in parentheses to the right of each compound.

CH4 (g) + 2 O2 (g) #

1C

4 O

4H

CO2 (g) +

1C 2 O

2 H2O (g)

2 O 4H

Coefficients are inserted to balance the equation.

answer answer

Slide 19 / 142 Subscripts and Coefficients

Subscripts tell the number of atoms of each element in a molecule. Coefficients tell the number of representative particles (atoms, molecules, or formula units).

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4 How many nitrogen atoms are in one formula unit of ammonium sulfate?

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3 How many oxygen atoms are in one formula unit of calcium nitrate? (First, write the formula for calcium nitrate.)

A2 B3 C5 D6 E I don't know how to answer this.

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Balancing chemical equations

Write a balanced chemical equation for this reaction. First write a skeleton equation

chlorine + sodium bromide # bromine + sodium chloride Cl2 + NaBr # # Br2 + NaCl

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Balancing chemical equations

Then, count up the number of each type of element on each side of the reaction

Cl2 + NaBr # # Br2 + NaCl

Reactants

Products

Cl: 2

Cl: 1

Na: 1

Na: 1

Br: 1

Br: 2

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Balancing chemical equations

Next, identify one element that is not balanced. It is best to start with an easy element. The fewer places an element appears on

both sides of a reaction, the easier it will be to balance.

Cl2 + NaBr # # Br2 + NaCl

Reactants

Products

Cl: 2

Cl: 1

Na: 1

Na: 1

Br: 1

Br: 2

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Balancing chemical equations

Identify the side that needs more of that particular element.

Cl2 + NaBr # # Br2 + NaCl

Reactants

Products

Cl: 2

Cl: 1

Na: 1

Na: 1

Br: 1

Br: 2

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Balancing chemical equations

Determine which molecule or element will be getting the coefficient. In this case, because we need more chlorine on the products side, we will have to add a coefficent to the NaCl, since

that is the only product containing chlorine.

Cl: 2 CNl:a2: 1 NBar:: 11 Br: 1

Cl2 + NaBr # # Br2 + NaCl

Reactants

Products

Cl: 1

Na: 1

Br: 2

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Balancing chemical equations

Now, just reevaluate the amount of each element on the table

Cl: 2 CNl:a2: 1 NBar:: 11 Br: 1

Cl2 + NaBr # # Br2 + 2NaCl

Reactants

Products

Cl: 1 2

Na: 1 2

Br: 2

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Balancing chemical equations

To figure out what the coefficient should be, simply take the amount of

that specific element you need from the molecule, and divide by the amount of the element you have in the molecule.

Cl: 2 CNl:a2: 1 Na: 1 Br: 1 Br: 1

Cl2 + NaBr # # Br2 + __2NaCl

Reactants

Products

Cl: 1

Na: 1

Br: 2

Need Have

=

2 1

=

2

If this is not a whole number, simply multiply ALL the substances in the reaction by some whole number to make the coefficients

whole numbers.

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Balancing chemical equations

Continue with these steps until all the elements are balanced. When all the elements exist in equal amounts on both sides of the

equation, you have a balanced chemical equation.

Cl2 + 2NaBr # # Br2 + 2NaCl

Cl: 2 Reactants

Products

CNl:a2: 1

Cl: 1 2

NBar:: 11 2

Na: 1 2

Br: 1 2

Br: 2

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Balancing chemical equations

SPECIAL NOTE: Make sure that when you are calculating your coefficents you are only looking at the amounts needed/had by

individual elements or molecules

CH3OH + O2 # # CO2+ 2H2O

Cl: 2 Reactants

CN:a1: 1 HB:r:41 O: 1+2=3

Products

C: 1 H: 2 4 O: 2+1=3 2+2=4

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Balancing chemical equations

SPECIAL NOTE: Here is the incorrect way to evaluate the coefficent in this case

CH3OH + O2 # # CO2+ 2H2O

Cl: 2 Reactants

CN:a1: 1 HB:r:41 O: 1+2=3

Products

C: 1 H: 2 4 O: 2+1=3 2+2=4

Need Have

=

4 3

=

WRONG!!!

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Balancing chemical equations

SPECIAL NOTE: Here is the correct way to evaluate the coefficent in this case

CH3OH + O2 # # CO2+ 2H2O

Cl: 2 Reactants

CN:a1: 1 HB:r:41 O: 1+2=3

Products

C: 1 H: 2 4 O: 2+1=3 2+2=4

Because we already have 1 Oxygen

Need Have

=

4 - 1 2

=

from CH3OH, we only need 3 Oxygen from O2

Because O2 only has 2 Oxygen, the

3 2

denominator must be 2.

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Balancing chemical equations

If you follow these steps, you'll be able to balance any type of reaction.

2CH3OH + 3O2 # # 2CO2+ 4H2O

Cl: 2 Reactants

CN:a1: 12 HB:r:41 8 O: 1+2=3 2+6=8

Products

C: 1 2 H: 2 4 8 O: 2+1=3 2+2=4 4+4=8

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Balancing chemical equations

SPECIAL NOTE: Remember to make sure you get rid of ALL fractions.

2CH3OH

+

2x

3 2

O2

# # 2CO2+

2x2H2O

Cl: 2 Reactants

CN:a1: 12 HB:r:41 8 O: 1+2=3 2+6=8

Products

C: 1 2 H: 2 4 8 O: 2+1=3 2+2=4 4+4=8

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5 When the following equation is balanced, the coefficients are:

Na + O2 # Na2O

A 1, 1, 1 B 1, 2, 4 C 4, 1, 2 D 2, 2, 1 E 4, 1, 4

answer

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6 When the following equation is balanced, the coefficients are

HgO #

Hg +

O2

A 1, 1, 1

B 1, 2, 4

C 4, 1, 2

D 2, 2, 1

E 4, 1, 4

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8 When the following equation is balanced, the coefficients are

NaCl +

CaI2 #

NaI +

CaCl2

A 1, 1, 1, 1 B 3, 2, 2, 3

C 2, 3, 2, 3

D 1, 3, 1, 2 E 2, 1, 2, 1

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10 When the following equation is balanced, the coefficients are

Al(NO3)3 +

Na2S #

Al2S3 +

NaNO3

A 2, 3, 1, 6 B 2, 1, 3, 2

C 1, 1, 1, 1 D 4, 6, 3, 2

E 2, 3, 2, 3

answer

answer

answer

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7 When the following equation is balanced, the coefficients are

Al + ZnCl2 #

Zn + AlCl3

A 1, 1, 1, 1 B 4, 7, 4, 6

C 2, 3, 2, 3 D 1, 3, 1, 2 E 2, 3, 3, 2

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9 When the following equation is balanced, the coefficients are

NH3 +

O2 #

NO2 + H2O

A 1, 1, 1, 1

B 4, 7, 4, 6 C 2, 3, 2, 3 D 1, 3, 1, 2 E 4, 3, 4, 3

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Reaction Types

Most reactions can be classified as one of the following:

Precipitation: formation of insoluble product out of aqueous solutions

Oxidation/Reduction: exchange of electrons between atoms/ions

Acid/Base: reaction between acids and bases

answer

answer

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Precipitation Reactions

Slide 44 / 142 Precipitation Reactions

The giant clam's shell is made from the precipitation of CaCO3

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Slide 45 / 142 Precipitation Reactions

Precipitation reactions involve the reaction of water soluble ionic compounds to form a water insoluble product called a precipitate:

AgNO3(aq) + HCl(aq) --> AgCl(s) + HNO3(aq)

AgCl precipitate

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11 Which one of the following would be INSOLUBLE in water? A Na2CO3 B NH4NO3 C AgNO3 D Mg(OH)2 E KCl

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Precipitation Reactions

One must know which ionic compounds are water soluble and which are not. It is the insoluble ones that form precipitates!

Some general rules apply:

ALWAYS SOLUBLE

NH4+, C2H3O2-, ClO3-, Group 1 A metal ions, NO3-

SOMETIMES SOLUBLE

Cl-,Br-, I- except when combined with Ag+, Hg+, and Pb2+

SO42- except when combined with Ag+, Hg+, Pb2+, Ca2+, Sr2+, Ba2+

INSOLUBLE

(unless paired with a soluble ion)

CO32-, PO43-, OH-, S2-, F-, O2-

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12 Which of the following would be MOST SOLUBLE in water?

A CaSO4 B PbF2 C PbI2 D Cu(OH)2 E CuSO4

answer answer

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