Chapters
6, 7, and 8
Writing
Balanced Chemical Equations
Predicting Products of a Chemical Reaction.
6:1,2,3 Chemical Reactions and Writing Balanced
Chemical Equations. S 12 3 2
Chemical Equations:
Evidence for a chemical reaction
Parts of a chemical equation: Reactants à Products (à , yields or produces. Catalyst on arrow)
Law of Conservation of mass: Atoms are neither created nor destroyed, only rearranged. Balance of atoms.
Ex. 3.0 g of Na + 2.1 g S = 5.1 g of Na2S
*Phase Notation: solid (s), if product (ê ), (ppt.), precipitate
Liquid (l)
Gas (g), if product (é)
Dissolved in water (aq), aqueous
*Write one phase for each pure substance. Do not indicate it for each element in a compound
Endothermic (+DH, heat is a reactant) and exothermic (-DH, heat is a product).
Coefficients used to balance atoms. Ex. “3 Al2(SO4)3 bookkeeping
Example: Photosynthesis 6 CO2(g) +
6 O2(g) -----------
> C6H12O6(aq) + 6 H2O(l)
Show balance of reactants and product atoms as a bookkeeping table
Assignment: Write a balanced equation and structural (show atoms with balls) diagram equations for:
a.) 3 Cl2, 2 Fe, 5 H2O
b.) nitrogen and hydrogen make ammonia Ex. on display screen
c.) zinc and hydrochloric acid produces hydrogen gas and zinc chloride
d.) carbon reacts with oxygen to produce carbon dioxide
e.)
sodium chloride is broken down into its elements
Guidelines for Balancing Chemical
Equations by Inspection (Trial and Error):
1. Identify the reactants and products and write their correct chemical formulas. Write the unbalanced equation.
2. Balance most complex atoms first. Use coefficients only. Never change a formula’s subscripts
3. Balance the polyatomic ions if they appear on both the reactant and product side.
4. Complete balancing of all other atoms. Usually H and O can be done last. They seem to balance themselves.
5. Reduce coefficients to simplest whole numbers
Homework Practice:
Worksheet; Side 1. Balance the equations with coefficients
Text
Problems to be Completed on the Other Side of this
Worksheet:
*P. 172 #20,
31,45,49,53,54,56,57,58,63,65,66,67,70,71
*(Although
the directions may say to write an “unbalanced” equation, write a balanced
equation for each.)
Chapter 7:
Describing Reactions and Predicting the Products of
Chemical Reactions
5 Major Types of Chemical Reactions and Evidence of a Reaction:
1.
Double Displacement Reactions (Metathesis): Chapter
7
2 compounds react by switching ions. Ionic charges do not change.
In general: AB + CD à AD + BC
3 Types of evidence: Formation of a solid precipitate, Neutralization produces water, formation of a gas.
Prelude: Anionic salt, when placed in water, dissociates “breaks up” into ions. A positive cation and a negative anion. Ex’s. Write Products of Dissociation for the following salts:
NaCl à Na+ + Cl-
K2SO4 à 2K+ + SO42-
AlCl3 à Al3+ + 3 Cl-
NH4Cl à
Mg(NO3)2 à
Fe2(SO4)3 à
Solubility Rules (distribute): Solubility Rules
Decide if the following salts are soluble or insoluble in water: See P. 195 #11-14
a.) CaSO4
b.) etc.
A. Precipitation Reaction: formation of a solid precipitate:
Introductory Discussion:
(listen, don’t worry about note taking.)
Pure water does not conduct an electric current. A non-electrolyte. Demonstrate with conductivity apparatus. When ionic substances are placed in water they dissociate and as free ions would conduct an electric current, electrolytes. Most ionic materials only contain two types of ions. Ex. When ions of AgNO3 are placed in solution they appear as (Ag+ and NO3-). In a separate beaker ions of NaCl appear as Na+ and Cl-. If these 4 ions are mixed a solid precipitate is formed. What possible identity could the solid have? Rationalize with possibilities. Introduce Solubility Rules (P.183, Table 7.1 and back cover of textbook). Discuss solubility rules handout to distinguish soluble (disappears) Vs, Insoluble (remains undissolved) salts.
Write balanced equation with phase notation for reaction of silver nitrate and sodium chloride.
B. Neutralization Reaction: Formation of water
Acids and bases neutralize to form salt and water. Acid + Base à Ionic Salt and Water
Both are electrolytes. Net ionic: H+ + OH- à H2O
|
|
Acids |
Bases |
|
Taste |
Sour |
Bitter |
|
Arrhenius |
Produces H+ (proton) in solution |
Produces |
|
Ex. |
HCl, HNO3, H2SO4, see ion sheet |
NaOH, KOH, NH3, Ba(OH)2 |
|
Litmus |
Red |
Blue |
|
pH |
Below 7 |
Above 7 |
Ex. Reaction of hydrochloric acid and potassium hydroxide, with phase notation
Ex. Reaction of sulfuric acid and sodium hydroxide, with phase notation
C. Formation of a gas.. Gas escapes as bubbles
Ex. Decomposition of carbonates: PbCO3(s) à PbO(s) + CO2(g)
Ex. “Volcano”; HC2H3O2(aq) + NaHCO3(s) à NaC2H3O2(aq) + CO2(g) + H2O(l)
Homework Practice:
P. 195, #3,9,11,12,15,18,
21,31,33,34,35,36,39
Chapter
8: Describing Reactions
and Predicting the Products of Chemical Reactions
Major Types of Chemical Reactions and Evidence of a Reaction:
B. Oxidation-Reduction Reactions (Transfer of electrons. Oxidation numbers change) Chapter 8
· Recall that metals lose e- (cation) and non-metals gain e-(anion).
· Clues; Metal and Non-metal to produce an ionic compound, rusting, fuel burning, thermite!
· Review of periodic table: major trends of ions
|
Column I |
Column II |
Column III |
|
Column VI |
Column VII |
|
Lose 1 electron |
Lose 2 electrons |
Lose 3 electrons |
|
Gain 2 electrons |
Gain 1 electron |
|
+1 cation |
+2 cation |
+3 cation |
|
-2 anion |
-1 anion |
|
|
|
|
|
|
|
2. Synthesis (Combination): 2 pure elements or small compounds that create a larger compound on the product side.
Ex. 2 Na(s) + Cl2(g) à 2 NaCl(s), Uncharged neutral atoms develop a charge in compound.
Demo: Write for
burning of magnesium ribbon with phase notation: Mg(s) + O2(g)
à MgO(s)
3. Decomposition (Analysis): A compound (never an element) is broken down into simpler substances, usually accomplished with heat or electric current.
Ex. 2 HgO(s) à 2 Hg(l) + O2(g)
Demo: Write for
decomposition by heating of KClO3.
2 KClO3(s) à 2 KCl(s) + 3 O2(g)
4. Combustion: Involve oxygen and produce heat so rapidly that a flame results.
Ex. CH4(g) + 2O2(g) à CO2(g) + 2H2O(g)
Demo: Gummy Bear into
the hot KCl / O2 from decomposition.
C6H12O6(s) + 6O2(g) à 6CO2(g) + 6H2O(g)
5. Single Displacement Reaction: Element and compound combine. The element replaces the similar type of ion in the compound. A + BC à AC + B, A and B are metals.
Ex. Zn(s) + 2HCl(aq) à ZnCl2(aq) + H2(g) With metal element as reactant
Ex. F2(g) + KCl(aq) à KF(aq) + Cl2(g) With non-metal element as reactant
Demo: Write for Cu
wire in solution of silver nitrate. Cu(s) + AgNO3(aq) à Cu(NO3)2 + Ag(s)
Glencoe Video
Demonstration. Chapter 6, Section 2, Video 1 and Video 2
Homework Practice:
Text P.214-217,
#1,2,4,5,6,15,21,27, 28, 33,35,36,37,48
Laboratory: Writing
Balanced Chemical Equations Based on Observations of Chemical Reactions
A series of different reactions are performed. The student must record all observations, classify the type of reaction, predict the products, and write a balanced equation with phase notation.
Eight different experiments are performed at each lab station.
Comprehensive Review, Chapters 6,7, and 8
Mini-Lab, "The Four Bottle Experiment"
Mini-Lab, Identify the contents of a bottle from observations of reactions
Worksheet: Chemical Reactions and Equations. Concepts, Writing, and Overall Review.
Chapters
6,7,8 Test.
Chemical Equations
Allow students the bulk of time to complete test as needed. They may use periodic table, ion sheet, and solubility rules handout.
After Test: Read 9:1 Counting by Weighing. Answer P.251, #1,2