1. Ch. 7 Outcomes Recognize some general signs of chemical reactions.
Distinguish reactants from products in a reaction (expressed in either words or chemical formulas)
Translate between word and formula equations and formulate one from the other.
Solve for correct balancing of a given chemical equation.
Recognize acids and bases from their chemical formulas.
Recognize and categorize chemical reactions by their type(s)
Precipitation, gas evolution, acid-base (neutralization), redox
Synthesis, decomposition, single and double replacement, combustion
Identify what is oxidized and what is reduced from an equation.
Formulate the complete combustion equation when given the hydrocarbon.
Predict products from given reactants and formulate complete chemical equation.
Balance completed chemical equation.

2. Beautifulchemistry.net

3. Evidence of chemical reaction
Chemical Change?
Precipitation
Precipitate- insoluble solid (more later)
Color change
Gas evolution
Light emission
Heat transfer
Is ice melting a chemical reaction?
Is any phase change a chemical reaction?

4. Chemical Equations To describe chemical reactions both
Qualitatively- what are reacting & what are formed
Quantitatively- how much of each is involved
𝑎 𝐴 (𝑠) + 𝑏 𝐵 (𝑙) 𝑐 𝐶 (𝑔) + 𝑑 𝐷 (𝑎𝑞)

5. Reading Chemical Equation
Reactants: left-hand side (A, B)
Products (pdts): right-hand side (C, D)
Coefficients: numbers indicates number of moles of each chemical (a, b, c, d)
Phase of chemicals: shown in ( ), solid, liquid, gas and aqueous.
: reads as “reacts with” on the reactant side
: reaction arrow, read as “to form” or “yields”
: equilibrium arrow
Reaction condition can represented above the reaction arrow. ( is heat)
Catalyst can be represented above the reaction arrow. (Pt is a catalyst) Pt
𝑎 𝐴 (𝑠) + 𝑏 𝐵 (𝑙) 𝑐 𝐶 (𝑔) + 𝑑 𝐷 (𝑎𝑞)

6. Examples of Words Equations
Potassium iodide solution reacts with lead (II) nitrate solution to form lead (II) iodide solid and potassium nitrate solution.
Iron reacts with oxygen gas to form solid iron(III) oxide.
Na (s) + H2O (l) NaOH (aq) + H2 (g)
Water decomposes into hydrogen gas and oxygen gas.
KI (aq)
+ Pb(NO3)2 (aq)
PbI2 (s)
+ KNO3 (aq)
Fe (s) + O2 (g) Fe2O3(s)
Sodium reacts with water to yield sodium hydroxide solution and hydrogen gas.
H2O (l)
H2 (g)
+ O2 (g)
Matter conservation is not observed in these equations.
More about that later.

7. Balancing equations Practice Key is to Matter/mass is conserved
the number of each type of atoms on both side of the reaction arrow has to equal.
When balancing equation
Only coefficient are adjusted, chemical formulae must not be changed
Changes quantity (amount of chemicals) not identity
Step 1- Write an unbalanced chemical equation using chemical formulas.
Step 2- Adjust coefficients to balance compounds.
Step 3- Adjust coefficients to balance free elements.
Step 4- Simplify coefficient to lowest whole-number ratios.
Step 5- Check that number and charge are balanced on both sides.
Step 6- Repeat Steps 2-5 if necessary.
Practice
Key is to

8. Examples 2 2 4 3 2 2 2 2 2 2 KI (aq) + Pb(NO3)2 (aq) PbI2 (s)
+ KNO3 (aq) 2 4 3 2
Fe (s) O2 (g) Fe2O3(s) 2 2
Na (s) H2O (l) NaOH (aq) H2 (g) 2 2
H2O (l) 2
H2 (g)
+ O2 (g)

9. Types of Reactions Acid-base Reactions (Neutralization)
Acid + Base Water + Salt
HCl
+ NaOH
+ NaCl
HOH
acidic
basic
neutral
Salt is not just table salt (NaCl)
Salt is any water soluble ionic compound.

10. Polyprotic acids/Polyhydroxy bases
Some acids can yield more than 1 H+.
Some bases can yield more than 1 OH-.
A2-
H3A  3 H+ + A-
A3-
Ex.
Ex.
B(OH)2  B OH-
Ex.
Ba(OH)2  Ba OH-
Ca(OH)2  Ca OH-

11. Precipitation Precipitate- insoluble solid Precipitation reaction
2 solutions (aqueous) reacts to form an insoluble species (solid)
KI (aq)
+ Pb(NO3)2 (aq)
PbI2 (s)
+ KNO3 (aq)

12. Gas-Evolution Reactions
When gaseous product is formed upon the reaction of two aqueous solutions.
Direct product-
Intermediate decomposition-
Bubbles out of the solution
intermediate
decomposition

13. Redox Reactions LEO the lion goes GER
Rxns in which electrons transfer from one reactant to another.
Lose electron- oxidation
Gains electron- reduction
LEO the lion goes GER
Lose Electrons Oxidation
Gain Electrons Reduction
Oxidation and Reduction are reverse of each other
A(s)  A e-
A2+ + 2e-  A(s)
A(s) is oxidized to A2+
A2+ is reduced to A(s)

14. Redox Reaction A(s)  A2+ + 2e- A2+ + 2e-  A(s)
Half reactions (describes the change of one of the chemical species)
- oxidation half rxn?
- reduction half rxn?
Identify the following half rxns as either oxidation or reduction
Na(s)  Na+ + e-
Cl2 (g) + 2 e-  2 Cl-
Put oxidation and reduction half rxns together to get a full equation
2 Na(s) + Cl2(g)  2 Na+ Cl-

15. Redox Reaction 2 Na(s) + Cl2(g)  2 Na+ Cl-
Na(s) is oxidized to Na+
2 Na(s) + Cl2(g)  2 Na+ Cl-
Cl2(g) is reduced to Cl-
Need to clearly indicate the species
- Na (s) vs Na+
- Cl2 (g) vs Cl-

16. Combustion Reaction Will only focus on combustion of hydrocarbons.
Hydrocarbons- contains carbon and hydrogen (oxygen is optional).
Combustion requires O2(g) (this is available readily)
Produces carbon dioxide and H2O.
Balance equation: 1. carbon, 2. hydrogen, 3. oxygen, simplify.

17. Type of Reactions- Synthesis Reaction
More than one substances combine to form one more complex substance.
more than 1 substances
1 substance
Two moles of hydrogen gas reacts with one mole of oxygen gas
to form 2 moles of water.
Magnesium metal reacts oxygen gas to yield solid magnesium oxide.

18. Type of Reactions- Decomposition Reaction
Decomposition is the process of breaking down a compound into simpler compounds.
Examples-
Water decomposes into hydrogen gas and oxygen gas.
Calcium carbonate decomposes into calcium oxide and carbon dioxide.
Think of as the reverse of synthesis
1 substance
more than 1 substances

19. Type of Reactions- Single Replacement Reaction
One element replaces another element in a compound.
Cation replacement
Anion replacement
Examples
A & C form cations
B & D form anions
Why will A not bond with C?
Why will B not replace D?
Note: not balanced

20. Type of Reactions- Double Replacement Reaction
Cations and anions of two different ionic compounds switch “partners.”
Thought process:
A with B  no change
A with C  both cations
A with D  AD
AB + CD  AD + CB
Examples
Sulfuric acid reacts with lithium sulfide to form dihydrogen sulfide gas and lithium sulfate.
Hydrochloric acid reacts with sodium hydroxide to form water and sodium chloride.
Lead(II) nitrate reacts with sodium iodide to form solid lead(II) iodide and sodium nitrate.

21. ID Type of Rxns Exercise
2 Li(s) + Cl2(g)  2 LiCl(s)
Synthesis (redox rxn)
Pb(NO3)2 (aq) + 2 LiCl(aq)  PbCl2(s) + 2 LiNO3(aq)
Double replacement (precipitation)
2 CH3OH(l) + 3 O2 (g)  2 CO2(g) + 4 H2O(g)
Combustion of hydrocarbon
CuCl2(aq)  Cu(s) + Cl2(g)
Decomposition (redox rxn)
2 Al + Fe2O3  Al2O3 + 2 Fe
Single replacement (redox rxn)

22. Writing, balancing and predicting rxns
solid iron(III) oxide reacts with hydrogen gas.
Sulfur dioxide gas reacts with oxygen gas.
Ethanol (C2H6O) reacts with oxygen gas. 3 3
Fe2O3(s) H2(g) 2
 Fe(s) H2O
Single replacement C C B A A B 2 2
SO2(g) O2(g)
 SO3(g)
Synthesis A B C 3
C2H6O O2(g) 2
 CO2(g) H2O(g) 3
Combustion of hydrocarbon