Transcript Final Review: L17-25

Final Review: L17-25
Chem 11 Fall 2006
Balancing Equations
 4 ways to understand if a chemical reaction
occurred:
1. A gas is detected.
2. A precipitate is formed.
3. A permanent color change is seen.
4. Heat or light is given off.
 An exothermic reaction gives off heat and an
endothermic reaction absorbs heat.
Balancing Equations
 There are 7 elements that exist as diatomic molecules:
– H2, N2, O2, F2, Cl2, Br2, and I2
 When we balance a chemical equation, the number of
each type of atom must be the same on both the
product and reactant sides of the equation.
 We use coefficients in front of compounds to balance
chemical reactions.
Net Ionic Equations
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
The total ionic equation is:
H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) → Na+(aq) + Cl-(aq) + H2O(l)
Na+ and Cl- appear on both sides of the equation. They are
spectator ions. Spectator ions are in the solution, but do not
participate in the overall reaction.
Cancel out the spectator ions to get the net ionic equation.
The net ionic equation is:
H+(aq) + OH-(aq) → H2O(l)
Oxidation-Reduction Reactions
Oxidation reduction type of reactions involve transfer of
electrons from one substance to another.
Rusting of iron.
Iron metal reacts with oxygen in air to produce ionic iron(III) oxide
compound, which is composed of Fe3+ and O2- ions.
4 Fe(s) + 3 O2(g) → 2 Fe2O3(s)
In this reaction:
a) Iron loses electrons and is oxidized
Fe → Fe3+ + 3 eb) Oxygen gains electrons and is reduced
O2 + 4 e- → 2 O2-
Rules for Oxidation Numbers
To determine oxidation numbers apply these seven rules:
1. In the free state, a metal or a nonmetal has 0 oxidation
number.
2. A monoatomic ion has an oxidation number equal to
its ionic charge.
3. Oxidation number of a hydrogen atom is usually +1.
Rules for Oxidation Numbers
4. Oxidation number of an oxygen atom is usually -2.
5. In a molecular compound, the more electronegative
element carries a negative oxidation number equal to
its charge as an anion.
6. In an ionic compound, the sum of the oxidation
numbers for each of the atoms in the compound is
equal to 0.
7. In a polyatomic ion, the sum of the oxidation
numbers for each of the atoms in the compound is
equal to the ionic charge on the polyatomic ion.
Classifying Chemical Reactions
Chemical reactions can be divided into five categories:
I. Combination Reactions
II. Decomposition Reactions
III. Single-Replacement Reactions
IV. Double-Replacement Reactions
V. Neutralization Reactions
Combination reaction, two simpler substances are
combined into a more complex compound.
2 Mg(s) + O2(g) → 2 MgO(s)
Decomposition reaction, a single compound is broken
down into simpler substances.
Single-replacement reaction, a more active metal
displaces a less active metal in a compound.
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
Double replacement reaction, two ionic compounds in
aqueous solution switch anions and produce two new
compounds. BaCl2(aq) + K2CrO4(aq) → BaCrO4(s) + 2 KCl(aq)
Neutralization reaction, is the reaction of an acid and a
base.
H2SO4(aq) + 2 KOH(aq) → K2SO4(aq) + 2 H2O(l)
Decomposition Reactions
Decomposition reaction, a single compound is broken
down into simpler substances.
2 HgO(s) → 2 Hg(l) + O2(g)
Ni(HCO3)2(s) → NiCO3(s) + H2O(l) + CO2(g)
CaCO3(s) → CaO(s) + CO2(g)
Mass Limiting Reactant Problem
How much molten iron is formed from the reaction
of 25.0 g FeO and 25.0 g Al?
3 FeO(l) + 2 Al(l) → 3 Fe(l) + Al2O3(s)
25.0 g FeO ×
1 mol FeO
71.85 g FeO
×
3 mol Fe
3 mol FeO
×
55.85 g Fe
1 mol Fe
= 19.4 g Fe
19.4 g Fe can be produced if FeO is limiting
reactant.
Cont’d…Mass Limiting Reactant
Problem
3 FeO(l) + 2 Al(l) → 3 Fe(l) + Al2O3(s)
1 mol Al
3 mol Fe
25.0 g Al ×
×
26.98 g Al
2 mol Al
55.85 g Fe
×
1 mol Fe
= 77.6 g Fe
77.6 g Fe can be produced if Al is limiting.
Describing a Gas
•
Gases are composed of tiny particles
•
The particles are small compared to the average
space between them
Assume the molecules do not have volume
•
Molecules constantly and rapidly moving in a
straight line until they bump into each other or
the wall
Average kinetic energy is proportional to the
temperature
•
Assumed that the gas molecules attraction for
each other is negligible
Gas Laws
Boyle’s Law states that the volume of a gas is inversely proportional
to the pressure at constant temperature.
P1V1 = P2V2
Charles Law states that the volume of a gas is directly proportional
to the temperature in Kelvin.
V1/T1 = V2/T2
Gay-Lussac discovered that the pressure of a gas is directly
proportional to the temperature in Kelvin.
P1/T1 = P2/T2
Combined Gas Law
P1V1/T1 = P2V2/T2
Cont’d…Review
 Boyle’s Law is:
P1V1 = P2V2
V2
V1
=
T2
T1

Charles’ Law is:

Gay-Lussac’s Law is:

The combined gas law is:
P2
P1
=
T2
T1
P1V1 P2V2
=
T1
T2
Intermolecular Bond Concept

An intermolecular bond is an attraction between
molecules.

In the intramolecular bonds, attraction is between
the atoms in a molecule.

Attraction strength between molecules determine
some of the liquid properties, such as vapor
pressure, viscosity, and surface tension.

Intermolecular bonds are much weaker than
intramolecular bonds.
Intermolecular Forces
•
There are three types of intermolecular bonds:
Dispersion forces
Dipole forces
Hydrogen bonds
•
Dispersion forces are the weakest and hydrogen bonds are
the strongest.
•
These intermolecular attractions affect the physical
properties of substances.