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CHEMISTRY EXAM 4
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Metallic substances are good conductors because their electrons move like a sea and vibrate
rapidly when they are heated, passing heat along
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Covalent and ionic compounds pass heat along using strings of atoms and ions, not electrons
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2 Temperature as a Property of Matter
Temperature is a quantitative measure
Can be measured on a relative (°Celsius and °Fahrenheit) or absolute scale (Kelvin)
Celsius → Kelvin = +273
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15 °C
Warmer = more movement
Vibrate, Rotate, & Translate = movement of molecules in space
Kinetic Energy = energy associated with the motion of molecules
Temperature is a measure of the average kinetic energy of the atoms, molecules, or ions in a
substance
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3 The States of Matter
Gas → Liquid → Solid = More kinetic energy → Less kinetic energy
Kinetic Molecular Theory = explains behavior of gases
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5 The Properties of Gases
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Expand to fill their containers
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6 Pressure vs
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The pressure of a gas increases as more gas is added to the container
a
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7 Atmospheric Pressure
In a glass tube bent in a U shape, with one side being filled with water and the other with ethyl
alcohol, the pressure of the water pushing down on one side of the tube is equal to the pressure of
the alcohol
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325 kPa = 0
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8 Boyle’s Law
Pressure is inversely proportional to volume when temperature and the number of moles of gas
are kept constant
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If the gas is
compressed without changing the temperature, the AKE remains the same
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An increase in collisions on the
walls of the container leads to an increase in the pressure of the gas
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9 Amonton’s Law
Pressure is directly proportional to temperature when volume and the number of moles of gas
are kept constant
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AKE rises when the particles move faster, which
means an increase in collisions
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Because volume is constant, surface area is constant
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Provided the definition of absolute zero
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AKE of the particles is proportional to the temperature of the gas
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If they move
faster, collisions increase and take on a larger impact, which leads to an increase in pressure
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12 Avogadro’s Hypothesis
Avogadro argued that Gay Lussac’s Law of combining volumes could be explained by assuming
that equal volumes of different gases collected under similar conditions contain the same
number of particles
Volume is proportional to the number of particle in the gas (V & n)
Equal volumes of different gases contain the same number of particles
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In a flexible container, the container would stretch, thus
increasing the volume
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08206)

T = temperature
The ideal gas equation can be used to predict the value of any one of the four variable that
describe a gas from known values of the other three (P, V, n, T)
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14 Dalton’s Law of Partial Pressure
P =P +P +P
P = n (RT/V) + n (RT/V) + n (RT/V) …
n =n+n+n …
total

total

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1

2

3

2

total

1

3

2

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Gases are composed of a large number of particles that behave like hard, spherical
objects in a state of constant, random motion
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The particles in a gas are much smaller than the distance between them, Volume is
mostly empty space
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Collisions are elastic
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The Average Kinetic Energy of a collection of gas particles depends on the
temperature of the gas and nothing else
Kinetic energy can be described as one-half of the product of its mass x the velocity squared:
KE = ½ mv
2

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Each time a particle hits the wall, it exerts a force on the wall
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A
change in force or surface area results in a change in pressure
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Effusion = the rate at which a gas escapes through a pinhole into a vacuum
The rate of effusion is inversely proportional to the square root of either the density or the
molecular weight of the gas
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1 Energy
[C H O + 6O → 6CO + H O]
Kinetic Energy = energy of motion
Potential Energy = energy of position
Transferred or converted from one object to another - never created nor destroyed
Thermodynamics = transfer of energy and the conversions between different forms of energy
associated with chemical reactions
Changes in energy that occur in a chemical reaction are due to the breaking and forming of bonds
Energy is released when bonds are formed and absorbed when bonds are broken
Breaking bonds requires an input of energy
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2

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Bond strength affects the amount of heat released in a chemical reaction
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Heat and the Kinetic Molecular Theory
System = small portion being tested
Surroundings = everything else
Boundary separates the system from the surroundings - can be rigid or elastic
Kinetic Theory of Heat = when heat enters a system, heat can increase the average motion
(AKE) with which the particles in the system move
Atoms are in constant motion
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Specific Heat = the amount of heat needed to raise the temperature of one gram of a substance by
one degree celsius
Molar Heat Capacity = the amount of heat needed to raise the temperature of one mole of a
substance by one degree celsius (used to compare equal numbers of particles)
1 cal = 4
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If equal amounts of heat are absorbed by an equal number of moles of two substances, there
will be a larger increase in the temperature of the substance with the smaller molar heat
capacity
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Change in Temperature = △T
△T = T - T
final

initial

To calculate the amount of heat given off or absorbed, need to know:
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Molar heat capacity OR the specific heat capacity of the substance
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5 State Functions
State Functions = depends only on the state of the system, not the path used to get to that state
Extensive Properties = properties that depend on the size of the sample (ex: mass and volume)
Intensive Properties = properties that do not depend of the size of the sample (ex: temperature
and density)
State Functions Include:
• Temperature
• Energy
• Pressure
• Volume
• Enthalpy

Only initial and final conditions matter for state functions
X is a state function if and only if △X is zero when the system returns to its initial state
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7 Work
Work of Expansion = work done by a system on its surroundings when the gas expands
Work done by a gas when it expands is equal to the product of the force (F) that is applied to the
piston times the distance the piston moves:
|w| = F · △x
This force is applied equally to every point on the surface area of the piston (A), resulting in a
pressure that is equal to the force per unit of area:
P = F/A
|w| = P · A · △x
|w| = P△V
w = -P△V
The increase in potential energy is equal to mg△h where:
m = mass of piston
g = acceleration due to gravity
△h = difference between the final and initial height of the piston
mg△h = -work
△E - work = -△E
gas

surroundings

7
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Calorimeter = unit for heat given off or absorbed by a chemical reaction
When keeping the system at a constant pressure, look for changes in the enthalpy
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64 kJ/mol ↠ EXOTHERMIC
2H O → 2H + O ↠ △H = +483
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10 Enthalpy as a State Function
Both energy and enthalpy are state functions
Example
When considering a reaction such as:
H + Cl → 2HCl
Visualize the reaction as if it occurred in two steps
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This step is
endothermic because bonds are being broken:
H + Cl → 2H + 2Cl
Next, assume the atoms recombine to form the product of the reaction
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7kJ/mol - 863
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5kJ/mol
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2

2

2

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All solutes have concentrations of 1 M
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9869 atm ~ 1 atm)
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13 Enthalpies of Atom Combination
It is important to remember while doing enthalpy calculations using atom combination data that
very few chemical reactions actually occur by first breaking all the bonds in the starting

materials to form isolated atoms in the gas phase, followed by recombination of the atoms to form
the products of the reaction
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15 Bond Length and the Enthalpy of Atom Combination
Strength of bonds is related to bond length
As bond length increases, bond strength decreases
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rxn

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