Chapter 9

Classifying Chemical Reactions

Types of Reactions

• We will consider five types of reactions :1. Single displacement reactions

2. Double displacement reactions

3. Decomposition reactions

4. Synthesis reactions

5. Combustion reactions

1. Single Replacement Reactions

• Single Replacement Reactions occur when one element replaces another in a compound.

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

• element + compound compound + elementA + BC AC + B (if A is a metal) ORA + BC BA + C (if A is a nonmetal)

(remember the cation always goes first!)

In a single replacement reaction it is better to write H2O as HOH because it will split into H+ and OH- (not H+ and O2- !!)

Single Replacement

• A small piece of lithium metal is added to water.

Single Replacement Reaction

Single Replacement Reactions

• Sodium chloride solid reacts with fluorine gas

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

unbalanced

Single Replacement Reactions

• Zinc metal reacts with aqueous nickel (II) nitrate

Zn(s)+ Ni(NO3)2(aq) Zn(NO3)2(aq) + Ni(s)

2. Double Replacement Reactions

• Double Replacement Reactions occur when the cations in two compounds switch places.

• compound + compound compound + compound

• AB + CD AD + CB

Double Replacement Reactions

• KOH + H2SO4 → K2SO4 + HOH

• FeS + HCl → FeCl2 + H2S

• NaCl + H2SO4 → Na2SO4 + HCl

• NH4NO3 + NaCl → NH4Cl + NaNO3

Decomposition Reactions

• Decomposition reactions occur when a compound breaks up into two or more substances.

• Some examples of decomposition reactions are:– Potassium chlorate when heated breaks into oxygen gas

and potassium chloride.

• 2KClO3 → 2KCl + 3O2

– Heating sodium bicarbonate decomposes into sodium carbonate and water and carbon dioxide.

• 6NaHCO3 → 3Na2CO3 + 3H2O + 3CO2

∆

∆

3. Decomposition Reactions• The simplest decomposition reactions

occur when a binary compound breaks up into its elements.

Compound Element + Element

• In general: AB A + B

• Example: 2 H2O 2H2 + O2

• Example: 2 HgO 2Hg + O2

Decomposition Reaction

This reaction is highly endothermic

Energy Changes

• “Many” decomposition reactions involve large changes in energy (they are highly endothermic or highly exothermic).

Toluene

A

A

A

Trinitrotoluene

Tri-Nitro-Toluene

Nitroglycerin

Nitroglycerin is a contact explosive (physical shock can cause it to explode) and it degrades over time to even more unstable forms. This makes it extremely dangerous to transport or use.

Alfred Nobel

• Nobel found that when nitroglycerin was added to an absorbent inert substance it became safer.

• He patented this in 1867 as dynamite.

Alfred Nobel “The Merchant of Death is Dead”

Alfred Nobel“The Merchant of Death is Dead”

• The erroneous publication in 1888 of a premature obituary of Alfred Nobel by a French newspaper, condemning him for his invention of dynamite, is said to have brought about his decision to leave a better legacy after his death.

• The obituary stated "The merchant of death is dead" and went on to say, "Dr. Alfred Nobel, who became rich by finding ways to kill more people faster than ever before, died yesterday.”

• In reality the newspaper had instead confused Alfred for his brother who had passed away.

Nobel Prizes

• Nobel signed his last will and testament and set aside the bulk of his estate to establish the Nobel Prizes.

Synthesis Reactions

• Synthesis reactions occur when two or more substances combine to form a compound. (Sometimes these are called combination or addition reactions.)

– sulfur trioxide reacts with water to make sulfuric acid.

• H2O + SO3 → H2SO4

4. Synthesis reactions• The simplest Synthesis reactions occur when

two elements combine and form a binary compound.

element + element compound• Basically: A + B AB

• Example: 2H2 + O2 2H2O

• Example: Fe + Cl2 FeCl2

Synthesis Reaction

5. Combustion Reactions

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

• This is also called burning!!!

• The products of combustion are carbon dioxide and water.

Combustion Reactions

• Example:

- CxHy + O2 CO2 + H2O

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

• Combustion also got you to school today.

Cellular RespirationCellular Respiration

CC66HH1212OO66 + 6O + 6O22 → →

6CO6CO22 + 6H + 6H22OO

Combustion Reactions• CxHy + O2 CO2 + H2O

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

Complete vs. Incomplete Combustion

• Determined by the amount of oxygen.

• Incomplete combustion occurs when there isn't enough oxygen to allow the fuel (usually a hydrocarbon) to react completely.

• Carbon monoxide and pure carbon will be produced in addition to carbon dioxide and water in incomplete combustion.

Gas Lighting and CO Poisoning

• People who lived in 19th century cities were often poisoned by exposure to carbon monoxide from illuminating gas, which was a flammable mixture of gas suitable for lighting purposes that is made from coal and contained extremely high levels of CO.  

Poe's face has one eye drooping lower than the other while his mouth slants the other way. This same abnormality can be seen in the faces of people poisoned by CO today.  It is caused by the effect of repeated CO exposure on facial nerves and can be partially if not completely reversed with months of daily oxygen therapy.(very high levels of CO exposure, in comparison, can cause complete paralysis or coma)

Was Poe suffering from CO poisoning or just a troubled soul?

• Poe described many symptoms of CO poisoning in his letters, poems and tales.

• People poisoned by CO often have the same bizarre physical and mental symptoms he describes.

Homework

• Reaction Type and Balancing Worksheet

(Due in two days).