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!)

When H2O splits into ions, it splits intoH+ 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

2NaCl(s) + F2(g) 2NaF(s) + Cl2(g)

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”

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 does cause some 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.

Combustion Reactions

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

Gas Lighting and CO Poisoning

Homework

• Reaction Type and Balancing Worksheet