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CHEMICAL REACTIONS

Reactants: Zn + I2 Product: Zn I2

- Page 321

Reactants

Products

Chemical Reaction or Change – process in which one or more substances are converted into one or more new substances.

Reactant - starting substance; on the left side of the reaction

Product – substance that is produced; on the right side of the reaction

Reactants --> Products

--> is read “yields”

Discuss breaking/forming bonds

In a chemical reaction the reactant's bonds break and the atoms are rearranged to form the products.

Chemical reactions may occur spontaneously which means without adding energy or non-spontaneously which means you must add energy for the reaction to occur.

Word Equation – a chemical equation using words (not formulas)‏

Ex. Calcium reacts with oxygen to produce calcium oxide

Formula Equation – a chemical reaction using formulas (not names)‏

Ex. Convert the above word equation to a formula equation:

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Example:

WORD EQN: Silver nitrate reacts with

copper to form copper (II) nitrate and silver

FORMULA EQN:

Example:

WORD EQN: hydrogen perioxide (H2O2) will

decompose into water and oxygen

FORMULA EQN:

BALANCING EQUATIONS:

Law of Conservation of Matter – Atoms are neither created nor destroyed in any chemical or physical process.

So...the number of atoms you start with (reactants) will be the same number of atoms you end

up with (products)...the only difference is the way in which they are all bonded together.

Coefficients – whole numbers placed in

front of a formula to indicate how many

units of that formula there are.

Balancing Examples: Chemical Equations Their Job: Depict the kind of

reactants and products and their

relative amounts in a reaction.

4 Al (s) + 3 O2 (g) ---> 2 Al2O3 (s)‏

The numbers in the front are called

stoichiometric coefficients.

The letters (s), (g), and (l) are the

physical states of compounds.

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–Chemical reactions occur when bonds

between the outermost parts of atoms are

formed or broken

–Chemical reactions involve changes in

matter, the making of new materials with

new properties, and energy changes.

–Symbols represent elements, formulas

describe compounds, chemical equations

describe a chemical reaction

Introduction

– Chemical equations show the conversion of reactants (the molecules shown on the left of the arrow) into products (the molecules shown on the right of the arrow).

• A + sign separates molecules on the same side

• The arrow is read as “yields”

• Example

C + O2 CO2

• This reads “carbon plus oxygen react to yield carbon dioxide”

Parts of a Reaction Equation

• The charcoal used in a grill is basically carbon. The carbon reacts with oxygen to yield carbon dioxide. The chemical equation for this reaction, C + O2 CO2, contains the same information as the English sentence but has quantitative meaning as well.

Because of the principle of the

conservation of matter,

an equation must be balanced.

It must have the same number of

atoms of the same kind on

both sides. Lavoisier, 1788

Chemical Equations

• Solid ___

• Liquid (l)‏

• Gas ___

• Aqueous solution (aq)‏

• Catalyst H2SO4

• Escaping gas ()‏

• Change of temperature ()‏

Symbols Used in Equations –When balancing a chemical reaction you

may add coefficients in front of the

compounds to balance the reaction, but

you may not change the subscripts.

• Changing the subscripts changes the

compound. Subscripts are determined

by the valence electrons (charges for ionic or sharing for covalent)‏

Balancing Equations

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Subscripts vs. Coefficients

• The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound.

Chemical Equations

4 Al(s) + 3 O2(g) ---> 2Al2O3(s)‏

This equation means

4 Al atoms + 3 O2 molecules

---produces--->

2 molecules of Al2O3

AND/OR

4 moles of Al + 3 moles of O2

---produces--->

2 moles of Al2O3

There are four basic steps to balancing a chemical equation.

1. Write the correct formula for the reactants and the products. DO NOT TRY TO BALANCE IT YET! You must write the correct formulas first. And most importantly, once you write them correctly DO NOT CHANGE THE FORMULAS!

2. Find the number of atoms for each element on the left side. Compare those against the number of the atoms of the same element on the right side.

3. Determine where to place coefficients in front of formulas so that the left side has the same number of atoms as the right side for EACH element in order to balance the equation.

4. Check your answer to see if:

– The numbers of atoms on both sides of the equation are now balanced.

– The coefficients are in the lowest possible whole number ratios. (reduced)‏

Steps to Balancing Equations Some Suggestions to Help You Some of Mr. Rapp’s Helpful Hints for balancing

equations:

• Take one element at a time, working left to

right except for H and O. Save H for next to

last, and O until last.

• IF everything balances except for O, and

there is no way to balance O with a whole

number, double all the coefficients and try

again. (Because O is diatomic as an element)‏

• (Shortcut) Polyatomic ions that appear on

both sides of the equation should be

balanced as independent units

Balancing Equations

___ H2(g) + ___ O2(g) ---> ___ H2O(l)2 2 ‏

What Happened to the Other

Oxygen Atom?????

This equation is not balanced!

Two hydrogen atoms from a hydrogen

molecule (H2) combines with one of the

oxygen atoms from an oxygen molecule

(O2) to form H2O. Then, the remaining

oxygen atom combines with two more

hydrogen atoms (from another H2 molecule)

to make a second H2O molecule.

Balancing Equations

___ Al(s) + ___ Br2(l) ---> ___ Al2Br6(s)3 2 ‏

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Balancing Equations

____C3H8(g) + _____ O2(g) ----

> _____CO2(g) + _____ H2O(g)‏

____B4H10(g) + _____ O2(g) ----

>

___ B2O3(g) + _____ H2O(g)

Balancing Equations Sodium phosphate + iron (III) oxide

sodium oxide + iron (III) phosphate

Na3PO4 + Fe2O3 ----

>

Na2O + FePO4

Types of Reactions

1. Synthesis – two or more reactants come

together to form a single product.

General:

Example:

Types of Reactions

Types of Reactions

2. Decomposition – a single reactant is

broken down into two or more products.

General:

Example:

Types of Reactions

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Types of Reactions

3. Single Replacement – an uncombined

element displaces an element that is part

of a compound.

General:

Example:

Types of Reactions

Types of Reactions

4. Double Replacement – atoms or ions

from two different compounds replace each

other.

General:

Example:

Types of Reactions

5. Combustion – when a hydrocarbon burns

in oxygen to produce carbon dioxide and

water.

General:

Example:

Sometimes the physical state of reactants

and products are indicated as follows:

(s) solid

(l) liquid

(g) gas

(aq) aqueous (means dissolved in water)‏

Example:

Sometimes reaction specifications or

conditions are written above the arrow.

Examples:

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PREDICTING PRODUCTS

1. Synthesis (you will only be responsible for ionic synthesis)‏

Ex1

Ex 2

Ex 3

PREDICTING PRODUCTS

2. Decomposition (you will only be responsible for elemental decomposition)‏

Ex. 1

Ex. 2

Ex. 3

PREDICTING PRODUCTS

3. Single Replacement (you will only be responsible for metal replacement)‏

Use the activity series to decide whether or not the single replacement reaction will occur or not.

Metals will only replace metals below them on the activity series.

Ex. 1

Ex. 2

Ex. 3

PREDICTING PRODUCTS

Ex. 4

Ex. 5

Ex. 6

Ex. 7

PREDICTING PRODUCTS

4. Double Replacement

A double replacement reaction occurs between two ionic compounds that are dissolved in water …aka ionic solution.

Remember that ionic compounds break into ions when dissolved in water.

Double replacement reactions are sometimes called

precipitation reactions because a precipitate is formed.

PREDICTING PRODUCTS

A double replacement reaction occurs ONLY IF

one of the products is insoluble.

The insoluble product is the precipitate because

it falls out of solution and makes the solution

cloudy and will eventually settle on the bottom.

Use the solubility rules to determine whether or

not the ionic products are soluble or insoluble.

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PREDICTING PRODUCTS

Ex. 1

Ex. 2

Ex. 3

Ex. 4

Types: Synthesis

Example C + O2

O O C + O O C

General: A + B AB

Types: Decomposition

Example: NaCl

General: AB A + B

Cl Na Cl + Na

Types: Decomposition

Example 2HgO

O Hg

O Hg

Hg

O O Hg

+

General: AB A + B

Types: Single displacement

Example: Zn + CuCl2

Zn Cl Cl

Cu +

General: AB + C AC + B

Cl Cl Zn

Cu +

Types: Double displacement

Example: MgO + CaS

General: AB + CD AD + CB

S O

Mg Ca +

O S

Mg Ca +

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Types of Reactions

There are millions of reactions.

Can’t remember them all

Fall into several categories.

We will learn 5 major 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

#1 - Combination Reactions

Combine - put together

2 substances combine to make one compound.

Ca +O2 CaO

SO3 + H2O H2SO4

We can predict the products if they are two

elements.

Mg + N2

Write and balance

Ca + Cl2

Fe + O2 iron (II) oxide

Al + O2

Remember that the first step is to write

the correct formulas

Then balance by using coefficients only

#2 - Decomposition Reactions

decompose = fall apart

one reactant falls apart into two or more

elements or compounds.

NaCl --> Na + Cl2

CaCO3 --> CaO + CO2

Note that energy is usually required to

decompose

#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 -->

#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 CO2 + ?

H2CO3(aq) CO2 + ?

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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

#3 Single Replacement

Metals replace other metals (and hydrogen)‏

K + AlN

Zn + HCl

Think of water as HOH

Metals replace one of the H, combine with

hydroxide.

Na + HOH

#3 Single Replacement

We can tell whether a reaction will happen

Some chemicals are more “active” than

others

More active replaces less active

There is a list on page 217 - called the

Activity Series of Metals

Higher on the list replaces lower.

#3 Single Replacement

Note the * concerning Hydrogen H can be replaced in acids by everything higher

Li, K, Ba, Ca, & Na replace H from acids and

water

Fe + CuSO4

Pb + KCl

Al + HCl

#3 - Single Replacement

What does it mean that Hg and Ag are on

the bottom of the list?

Nonmetals can replace other nonmetals

Limited to F2 , Cl2 , Br2 , I2 (halogens)

Higher replaces lower.

F2 + HCl

Br2 + KCl

A double replacement reaction occurs between TWO IONIC compounds that are DISSOLVED in WATER...aka IONIC SOLUTIONS.

Remember that IONIC compounds break into IONS when dissolved in water.

Double replacement reactions are sometimes called PRECIPITATION reactions because a PRECIPITATE is formed.

A double replacement reaction occurs ONLY IF one of the products is INSOLUBLE.

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The INSOLUBLE product is the PRECIPITATE because it FALLS out of solution and makes the solution CLOUDY and will eventually SETTLE on the bottom.

Use the SOLUBILITY RULES to determine whether or not the ionic products are SOLUBLE or INSOLUBLE.

#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 Fe+3 OH- + Na+1 Cl-1

NaOH + FeCl3 Fe(OH)3 + NaCl

#4 - Double Replacement

Has certain “driving forces”

Will only happen if one of the products:

doesn’t dissolve in water and forms a solid (a

“precipitate”), or

is a gas that bubbles out, or

is a covalent compound (usually water).

Complete and balance

assume all of the following reactions take

place:

CaCl2 + NaOH

CuCl2 + K2S

KOH + Fe(NO3)3

(NH4)2SO4 + BaF2

How to recognize which type

Look at the reactants:

E + E = Combination

C = Decomposition

E + C = Single replacement

C + C = Double replacement

Examples

H2 + O2

H2O

Zn + H2SO4

HgO

KBr +Cl2

AgNO3 + NaCl

Mg(OH)2 + H2SO3

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#5 - Combustion

Means “add oxygen”

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 (possibly just C) and H2O.

Examples

C4H10 + O2 (assume complete)‏

C4H10 + O2 (incomplete)‏

C6H12O6 + O2 (complete)‏

C8H8 +O2 (incomplete)‏

An equation...

Describes a reaction

Must be balanced in order to follow the Law of

Conservation of Mass

Can only be balanced by changing the

coefficients.

Has special symbols to indicate physical state,

and if a catalyst or energy is required.

Reactions

Come in 5 major 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.