Chapter 9 Classifying Chemical Reactions Types of Reactions

Chapter 9 Classifying Chemical Reactions

Types of Reactions • We will consider five types of reactions : 1. 2. 3. 4. 5. Single displacement reactions Double displacement reactions Decomposition reactions Synthesis reactions 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 + element 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 H 2 O splits into ions, it splits into H+ and OH- (not H+ and O 2 - !!)

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 2 Na. Cl(s) + F 2(g) 2 Na. F(s) + Cl 2(g)

Single Replacement Reactions • Zinc metal reacts with aqueous nickel (II) nitrate Zn(s)+ Ni(NO 3)2(aq) Zn(NO 3)2(aq) + Ni(s)

2. Double Replacement Reactions • Double Replacement Reactions occur when the cations in two compounds switch places. • compound + compound • AB + CD AD + CB

Double Replacement Reactions • KOH + H 2 SO 4 → K 2 SO 4 + HOH • Fe. S + HCl → Fe. Cl 2 + H 2 S • Na. Cl + H 2 SO 4 → Na 2 SO 4 + HCl • NH 4 NO 3 + Na. Cl → NH 4 Cl + Na. NO 3

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 ∆ • 2 KCl. O 3 → 2 KCl + 3 O 2 – Heating sodium bicarbonate decomposes into sodium carbonate and water and carbon dioxide. ∆ • 6 Na. HCO 3 → 3 Na 2 CO 3 + 3 H 2 O + 3 CO 2

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 H 2 O 2 H 2 + O 2 • Example: 2 Hg. O 2 Hg + O 2

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 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. • H 2 O + SO 3 → H 2 SO 4

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: 2 H 2 + O 2 2 H 2 O • Example: Fe + Cl 2 Fe. Cl 2

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: - Cx. Hy + O 2 CO 2 + H 2 O • Combustion is used to heat homes and run automobiles (example: octane in gasoline, is C 8 H 18). • Combustion also got you to school today.

Cellular Respiration C 6 H 12 O 6 + 6 O 2 → 6 CO 2 + 6 H 2 O

Combustion Reactions • Cx. Hy + O 2 CO 2 + H 2 O • 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