Download lecture 13

10/14/2014
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Today:
◦ Chemical Reactions:
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◦ Problem Set 4 DUE tonight at
11 pm
Combustions
Decompositions
Synthesis Reactions
Single Replacement Reactions
Double Replacement Reactions
 Precipitations & Solubility Rules
 Acid-Base Reactions
"It’s amazing that the body feeds the
brain sugar and amino acids and what
comes out is poetry and pirouettes.“
--Neurologist Robert Collins
Balancing Chemical Equations
Balancing chemical equations is an application of both the
Modern Atomic Theory and the Law of Conservation of Mass.
BALANCING EQUATIONS: The same number of each type of
element must occur on the left (BEFORE the reaction) and on
the right (AFTER the reaction)
CH4(g) + 2 O2(g)
CO2(g) + 2 H2O(g)
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Interpreting a Chemical Equation:
A chemical equation describes a chemical reaction much like a
sentence describes some action.
• Element Symbols → Letters
• Formulas → Words
• Equations → Sentences
(s)
=
Solid
(l)
=
Liquid
(g)
=
Gas
(aq)
=
Aqueous (dissolved in water)
+
=
"and"
=
"reacts to form" or "yields"
“The opportunity to bring about chemical change
deliberately for his own benefit arrived when man had
mastered the art of starting and maintaining a fire.”
–Isaac Asimov
Combustion Reactions:
• Combustion (aka “burning”): Reacting with OXYGEN (O2)
• A hydrocarbon (something containing Hydrogen and Carbon)
burns to produce carbon dioxide (CO2) and water (H2O)
• Special balancing rule for combustion:
Balance Carbon first, Hydrogen second, and Oxygen last.
DOUBLE CHECK
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Combustions: Reactions of a fuel with oxygen (O2)

Combustion often occurs with hydrocarbons (CxHy) to produce
CO2 & H2O:
BALANCE Oxygen last.
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Other substances can also combust (“burn”) in oxygen.
◦ Write the combustion of Iron metal to product Iron (III) Oxide
(aka “rust”)
◦ Write the combustion of Phosphorus (as P4) to form P4O10
Burning of Other Elements

Write the balanced equation for the combustion of Sulfur (S8) to
produce Sulfur Trioxide.
Burning Sulfur (aka “brimstone” as in “fire and brimstone”)
has been used as a fumigant to kill pests due to the toxicity of
the sulfur oxides.

Write the balanced equation for the burning of magnesium
metal.
Single Replacement Reactions:
Mg(s) + 2 HOH(l) → H2(g) +
Mg(OH)2(aq)
Magnesium fires require a
special type of fire
extinguisher (Class D)
designed specifically for
metal fires.
2 Mg(s) +
CO2(s) →
C(s)
+ 2 MgO(s)
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Single Replacement Reactions:
Decreasing EN
MORE REACTIVE
As electronegativity (EN) decreases…
the alkali metals become progressively MORE REACTIVE
2 Li(s) + 2 H2O(l) → 2 LiOH(aq) + H2(g)
2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g)
2 K(s) + 2 H2O(l) → 2 KOH(aq) + H2(g)
In the course of history, the discovery of single reactions has repeatedly
revolutionized human civilizations. The start of the Iron Age around 1300 B.C.
marked the moment we learned to transform brittle iron ores to iron metal.
This affected everything from how we grew food to how we waged wars.
Write the balanced chemical equation describing
iron (III) oxide reacting with carbon atoms to form
iron metal and carbon dioxide.
Thermite Reaction
• Write the balanced chemical equation describing iron (III) oxide reacting
with aluminum metal to form iron metal and aluminum oxide.
Fe2O3(s) + 2 Al(s) → 2 Fe(l) +
Al2O3(s)
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Decomposition: From One to Many

A single substance breaks into multiple simpler substances
 Example: Hydrogen peroxide decomposing…
 Example: Nitrogen triiodide decomposing…
SYNTHESIS
Sodium Chloride can be synthesized from sodium metal & chlorine gas:
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