Types of Chemical Reactions (rxns.). – Chemical reactions occur when bonds (between the electrons of atoms) are formed or broken – Chemical reactions

Types of Chemical Reactions (rxns.)Types of Chemical Reactions (rxns.)

– Chemical reactions occur when bonds (between the electrons of atoms) are formed or broken

– Chemical reactions involve changes in the chemical composition of matter

(the making of new materials with new properties) energy changes

– Symbols represent elements– Formulas describe compounds – Chemical equations describe a chemical reaction

IntroductionIntroduction

Types of ReactionsTypes of Reactions

• Reactions are classified by their products.• There are five types of chemical reactions we will

talk about:1. Synthesis reactions

2. Decomposition reactions

3. Single displacement reactions

4. Double displacement reactions

5. Combustion reactions

• You need to be able to identify the type of reaction and predict the product(s)

Steps to Writing ReactionsSteps to Writing Reactions

Some steps for doing reactions:1. Identify the type of reaction

2. Predict the product(s) using the type of reaction as a model

3. Balance it

Don’t forget about the diatomic elements! (BrINClHOF) For example, Oxygen is O2 as an element.

In a compound, it can’t be a diatomic element because it’s not an element anymore, it’s a compound!

Synthesis ReactionsSynthesis Reactions

Synthesis (meaning to make) are– Also called

Direct combination or combination reactions Addition reactions

– typified by their single product.

If you have a reaction in which at least 2 elements or compounds are reacted and produce a single product, the reaction is a synthesis reaction.

Synthesis ReactionsSynthesis Reactionsreactant + reactant 1 product

• Basically: A + B AB• Example: 2H2 + O2 2H2O

• Example: C + O2 CO2

• Note: Single Product! This is your clue that this is a synthesis or combination reaction.

Synthesis ReactionsSynthesis Reactions• Here is another example of a synthesis

reaction

Examples of Synthesis ReactionsExamples of Synthesis Reactions

2Na + S Na2S– This one is an example of two elements in

atomic form (Na and S) combining to form a compound (sodium sulfide).

2H2 + O2 2H2O– In this example, A and B are two elements in

molecular form (hydrogen and oxygen molecules), and the product is water, which is simply the chemical combination of hydrogen and oxygen.

Examples of Synthesis ReactionsExamples of Synthesis Reactions

4Fe + 3O2 2Fe2O3

– In this example, substance “A” is an element in atomic form (Fe), and substance “B” is an element in molecular form (O2). The result is a direct chemical combination of the two elements (FeO, iron oxide, which is “rust”).

CuO + H2O Cu(OH)2

– This is an example where both substances going into the reaction are molecules. The result is what you get when you “add” all of the atoms in the reaction together.

PracticePractice

• Predict the products. Write and balance the following synthesis reaction equations.

• Sodium metal reacts with chlorine gas

Na(s) + Cl2(g) • Solid Magnesium reacts with fluorine gas

Mg(s) + F2(g) • Aluminum metal reacts with fluorine gas

Al(s) + F2(g)

2 2 NaCl(s)

MgF2(s)

AlF3(s

)

2 3 2

Balanced

Decomposition ReactionsDecomposition Reactions

Decomposition reactions are really just the opposite of a synthesis reaction. Remember, if you can make a substance, you should be able to break it back apart into its components.

A good way to remember decomposition reactions to to remember what happens when something decomposes. It falls apart!


• Decomposition reactions occur when a compound breaks up into the elements or in a few to simpler compounds

• 1 Reactant Product + Product • Basically: AB A + B

• Example: 2 H2O 2H2 + O2

• Example: 2 HgO 2Hg + O2

• Note: Single Reactant! The single reactant is your clue that this is a decomposition reaction.


• Another view of a decomposition reaction:

Decomposition ExceptionsDecomposition Exceptions

• Carbonates and chlorates are special case decomposition reactions that do not go to the elements.• Carbonates (CO3

2-) decompose to carbon dioxide and a metal oxide

• Example: CaCO3 CO2 + CaO

• Chlorates (ClO3-) decompose to oxygen gas and a

metal chloride• Example: 2 Al(ClO3)3 2 AlCl3 + 9 O2

• There are other special cases, but we will not explore those in this class

PracticePractice

• Predict the products. Then, write and balance the following decomposition reaction equations:

• Solid Lead (IV) oxide decomposes PbO2(s)

• Aluminum nitride decomposes

AlN(s) 2

Pb(s) + O2(g)

Al(s) + N2(g)2

PracticePracticeIdentify the type of reaction for each of the

following synthesis or decomposition reactions, and write the balanced equation:

N2(g) + O2(g)

BaCO3(s)

Co(s)+ S(s)

2NI3(s)

PracticePracticeIdentify the type of reaction for each of the

following synthesis or decomposition reactions, and write the balanced equation:

N2(g) + O2(g)

BaCO3(s)

Co(s)+ S(s)

2NI3(s)

2 NO (g)

N2 (g) + 3I2 (s)

CoS (s)

BaO(s) + CO2 (g)

Single Replacement ReactionsSingle Replacement Reactions

Single replacement reactions occur when one chemical takes the place of another in a reaction.

In the typical single replacement reaction, an element trades places with one of the ions in a compound.


• A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-).

• element + compound product + product A + BC AC + B (if A is a metal) OR

A + BC BA + C (if A is a nonmetal) (remember the cation always goes first!)

When H2O splits into ions, it splits into

H+ and OH- (not H+ and O-2 !!)

Single Replacement ReactionsSingle Replacement Reactions• Another view:

The Activity SeriesThe Activity Series

Not all single replacement reactions will occur.

This depends upon the location of the elements present in the activity series

Elements above MAY replace elements below; elements below MAY NOT replace elements above them on the series

You will be given a copy of this!!!!


• Write and balance the following single replacement reaction equation:

• Zinc metal reacts with aqueous hydrochloric acid

Zn(s) + HCl(aq) ZnCl2 + H2(g)

Note: Zinc replaces the hydrogen ion in the reaction

[If ZnCl2 + H2(g) Zn(s) + HCl(aq) the reaction WOULD NOT OCCUR because Hydrogen is below zinc on the activity series]

2


• Sodium chloride solid reacts with fluorine gas

NaCl(s) + F2(g) NaF(s) + Cl2(g)

Note that fluorine replaces chlorine in the compound

• Aluminum metal reacts with aqueous copper (II) nitrate

Al(s)+ Cu(NO3)2(aq) Cu(s) + Al(NO3)3(aq)

2 2

2 3 3 2

Double Replacement ReactionsDouble Replacement Reactions

Double replacement reactions are identified by two ions trading places and forming new compounds.


• Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound

• Compound + compound product + product• AB + CD AD + CB

• Notice that one ion from compound AB replaces one ion from compound CD.


• Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together

• Example:

AgNO3(aq) + NaCl(s) AgCl(s) + NaNO3(aq)

• Another example:

K2SO4(aq) + Ba(NO3)2(aq) KNO3(aq) + BaSO4(s) 2

SolubilitySolubility

For a double replacement reaction to have occurred, a solid (precipitate) MUST be formed

There are rules to determine which of the materials formed is the solid

If no solid is formed, there is said to be no reaction.

Figure 8.4: The forming of solid AgCl.Figure 8.4: The forming of solid AgCl.

Solubility TablesSolubility Tables Solubility tables help determine which materials are soluble in

water and which are not In general, Solubility Rules can be summarized as follows

1. All compounds containing alkali metal cations and the ammonium ion are soluble.

2. All compounds containing NO3-, ClO4

-, ClO3-, and C2H3O2

- anions are soluble.

3. All chlorides, bromides, and iodides are soluble except those containing Ag+, Pb2+, or Hg2

2+.4. All sulfates are soluble except those containing Hg2

2+, Pb2+, Sr2+, Ca2+, or Ba2+.

5. All hydroxides are insoluble except compounds of the alkali metals, Ca2+, Sr2+, and Ba2+.

6. All compounds containing PO43-, S2-, CO3

2-, and SO32- ions are insoluble

except those that also contain alkali metals or NH4+.

You will be given a copy of this!!!!

PracticePractice

• Predict the products. Balance the equation1. HCl(aq) + AgNO3(aq)

2. Pb(NO3)2(aq) + BaCl2(aq)

3. FeCl3(aq) + 3NaOH(aq)

4. H2SO4(aq) + 2NaOH(aq)

HNO3(aq) + AgCl(s)

PbCl2(s) + Ba(NO3)2(aq)

Fe(OH)3(s) + 3NaCl(aq)

2 H2O(l) + Na2SO4(aq)

Combustion ReactionsCombustion Reactions

Combustion reactions are the ones that burn (or explode!). There are two types of combustion reactions—complete or incomplete reactions.

These reactions are identified by their products. They either produce carbon monoxide and water or carbon dioxide and water.

Complete Combustion ReactionsComplete Combustion Reactions

These reactions burn “efficiently” which means they produce carbon dioxide and water. These reactions typically burn cleanly and leave very little residue behind.


• Combustion reactions occur when a hydrocarbon reacts with oxygen gas.

• This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”:1) A Fuel (hydrocarbon)2) Oxygen to burn it with3) Something to ignite the reaction (spark)


• In general: CxHy + O2 CO2 + H2O

• Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide)

• Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C8H18)

Complete Combustion ReactionsComplete Combustion Reactions

CH4 + O2 CO2 + H2O

They may also be written:

CH4 CO2 + H2O

With O2 written above the arrow

Clues: CO2 (carbon dioxide) in the product along with water

O2

CombustionCombustion

• Example• C5H12 + O2 CO2 + H2O

• Write the products and balance the following combustion reaction:• C10H22 + O2

• C10H22 + O2

5 68

CO2 + H2O

10 11

2 31

20

22

CO2 + H2O

15.5

Incomplete Combustion ReactionsIncomplete Combustion Reactions

Incomplete combustion reactions occur when something does not burn efficiently. This can cause a lot of harm if the gases produced cannot escape. Carbon monoxide,an odorless and colorless gas, is dangerous. People poisoned by this gas usually become sleepy and can die due to exposure.

Incomplete Combustion ReactionsIncomplete Combustion Reactions

CH4 + O2 CO + H2O + CO2

These reactions may also be written by:

CH4 CO + H2O + CO2

Again, the O2 is usually written over the arrow.

Clue: CO (Carbon monoxide as a product.)

O2


Edgar Allen Poe’s drooping eyes and mouth are potential signs of CO poisoning.

Mixed PracticeMixed Practice

• State the type, predict the products, and balance the following reactions:

1. BaCl2 + H2SO4

2. C6H12 + O2

3. Zn + CuSO4

4. Cs + Br2

5. FeCO3

BaSO4 + HCl

CO2 + H2OZnSO4 + Cu

CsBr

FeO + CO2

Predicting Products of ReactionsPredicting Products of Reactions

Completing reactions requires knowledge of the different reaction types (sometimes called mechanisms).

You must first identify the reaction type by the reactants.

The only type of reaction that cannot be predicted this way is the combustion reaction since the products are very similar.

First Step:First Step:

Identify reaction type

Example:

Al + O2

Clue: 2 elements – Synthesis or combination reaction

Second Step:Second Step:

Write the net ionic equation for the reactants

Al + O2 becomes

Al3+ + O2-

Step 3Step 3

Using clues, complete reaction taking care to write each formula correctly by checking charges and “criss-crossing” if necessary.

Al + O2 Al3+O2-

Al + O2 Al2O3

Predicting Products of Reactions Predicting Products of Reactions (cont.)(cont.)

For Single Replacement reactions, check activity series to make sure the reaction goes.

Once you write the molecular equation, you should check for reactants and products that are soluble or insoluble. (Double Replacement only)

Documents

Types of Chemical Reactions (rxns.). – Chemical reactions occur when bonds (between the electrons of atoms) are formed or broken – Chemical reactions