FLVS Chemistry: Module 4.02- 4.05 Overview

Prior Information Needed

• Identify metals and nonmetals

• Identify polyatomic ions, oxides, chlorides

• Identify diatomic elements

• Write new ionic compound based on common charges

Overview of the Types of Reactions:

• Synthesis:  A  + B →  AB (Lesson 4.02)

• Decomposition:  AB → A + B  (Lesson 4.02)

• Combustion (2 different kinds, both have oxygen as reactant)

  • Inorganic Combustion

    • A  +  O₂  →  AO

  • Organic Combustion

    • CxHx  +  O₂ →  CO₂  + H₂O  

    • (CxHx can have any number as the subscripts.  Ex: CH₄, C₂H₄, C₆H₁₄)

• Single replacement:  A + BC → AC  + B  (Lesson 4.03)

• Double replacement:  AB  + CD  →  AD  + CB (Lesson 4.03)

• Acid-Base: AB  + CD  →  AD  + CB (Lesson 4.03)

• Redox: varies for general reaction (Lesson 4.04)

  • Note:  ALL reactions are redox also, except double replacement. 

4.02: Synthesis Reactions: A + B → AB (one product only)  

• Element + Element:  Metal with a nonmetal makes an ionic compound (salt)

  • Ca + Cl₂ → CaCl₂

• Element + Element: Two nonmetals form a binary molecule 

  • 2H₂ + O₂ → 2H₂O

• Compound + Water: Metal oxide plus water form a metal hydroxide 

  • CaO + H₂O → Ca(OH)₂

• Compound + Water: Nonmetal oxide plus water forms an oxyacid (ionic acid and oxygen)

  • SO₃ + H₂O → H₂SO₄

4.02: Decomposition Reactions: AB → A + B (one reactant only)

*To decompose; to break down. Can use electrolysis. 

• Binary compound decomposes  

  • 2NaCl → 2 Na + Cl₂

• Metal carbonate becomes a metal oxide and carbon dioxide

  • CaCO₃ → CaO + CO₂

• Metal chlorate becomes a metal chloride and oxygen gas 

  • 2KClO₃→ 2KCl + 3O₂

• Metal hydroxide becomes a metal oxide and water  

  • Ca(OH) ₂ → CaO + H₂O

• Oxyacid (acid and oxygen) makes nonmetal oxide and water

  • H₂SO₄ → SO₃ + H₂O

4.02: Combustion Reactions:

• Special type of redox reaction (all combustion are redox reactions)

• Oxygen, O₂, is always a reactant

• All combustion reactions produce a lot of energy

• Two different types:

1. Inorganic: A  +  O₂  →  AO   (Metal + oxygen gas)

Example: 2Ca + O₂ → 2CaO

2. Organic: CxHx  +  O₂ →  CO₂  + H₂O 

Note: CxHx can have any number as the subscript.  Ex:  CH₄, C₂H₄, C₆H₁₄

Example: CH₄ + 2O₂ → CO₂ + 2H₂O

4.03: Single Replacement Reactions: A + BY → AY + B

• Element + ionic compound → ionic compound + element

  
  

• More reactive element “replaces/switches places” with less reactive element

• Use Activity Series to determine if a reaction happens (from 4.03). Recall that we can use the periodic table as well.

• Need common charges and polyatomic ions from 3.02 and 3.04

Zn   +    MgCl₂    →     No reaction

Mg    +     ZnCl₂    → MgCl₂  +  Zn

 A      +      BY       →  AY     +   B

4.03: Double Replacement Reactions: AY + BZ → AZ + BY 

• Ionic compound + ionic compound → Ionic compound + ionic compound

• No activity series is needed, assume all react

• Need common charges and polyatomic ions from 3.02 and 3.04

• Ionic compounds trade ions forming usually a precipitate (solid), gas or water

Examples:

• Fe₂(SO₄)₃ + AlPO₄    →   FePO₄    +   Al₂(SO₄)₃

  • This is why:  Fe⁺³SO₄^-2 + Al^-2PO₄⁺³    →  Fe⁺³PO₄^-3 + Al^-2SO₄^-2

• MgO  +  Na₂S  →   MgS  + Na₂O

  • This is why: Mg⁺²O^-2  +   Na⁺¹S^-2 →   Mg⁺²S^-2  +   Na⁺¹O^-2

4.03: Acid-Base Reactions (Special type of Double Replacement):  

AY + BZ → AZ + BY

A special type of double replacement.  As such, these are generally not redox as well.  An acid reacts with a base.  Recall acids usually have an H⁺ ion at the beginning (HCl,  H₂SO₄) and a base has OH at the end (NaOH, LOH)

HCl   +   NaOH   →   NaCl   +  HOH

(Hint: Water, H₂O, can be written as HOH)

Acid   +     Base    →    Salt    +    Water

4.04: Reduction-Oxidation (Redox) Reactions:

• Transfers electrons between elements 

• The oxidation number is often the charge of the ion

• If there is a change of charge, redox has occurred. 

• LEO the lion goes GER….. Loss Electrons Oxidation…….Gain Electron Reduction

• They complement each other: You must have both.

• Example: 

Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g) (balanced equation)

Mg(s) +  H⁺ Cl⁻     →    Mg²⁺ Cl⁻ + H_2(g) (equation showing the ions)

Notice that magnesium changes its charge from zero to 2+. It lost two electrons to have an overall +2 charge.  LEO (Loss of Electrons is Oxidation).  Notice that hydrogen was an ion, and then is a neutral molecule H₂ (no charge; so hydrogen gains an electron and is reduced - GER Gain Electrons...Reduction (reduction of CHARGE which means to be “more negative” think of the number line… -2, -1, 0, 1, 2)

Diatomic Molecules: H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂

• Appear as a pair (diatomic) in nature

• Know these when writing and balancing equations

• Subscript 2 when the molecule is by itself in a reaction

  • 2NaCl→ 2Na + Cl₂

4.05: Nuclear Reactions

In nuclear reactions, a nucleus is split apart (fission) or two nuclei are combined (fusion). The identity of the element changes in these reactions because protons and neutrons are gained or lost by the atom over the course of the nuclear reaction.

• Fission - 

  • Nuclear power plants

  • During most fission reactions, an atom is bombarded with a neutron particle. In the example below, uranium-235 is the atom being bombarded. It becomes an unstable isotope of uranium, uranium-236. This isotope splits into barium, krypton, and three neutrons. With the smaller particles, there is a release of energy after the split.
    

• Fusion - 

  • The sun and other stars

  • For the fusion example below, two isotopes of hydrogen (deuterium has one neutron, and tritium has two neutrons) collide and fuse. This fusion reaction produces a helium nucleus (two protons and two neutrons) and a neutron particle. What is also released is a vast amount of energy.