Heat and Energy
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Energy can exist in different
forms, such as chemical,
electrical, electromagnetic,
thermal, mechanical, and
nuclear.
Kinetic energy – the energy of motion
Potential energy – the energy of position
(stored energy)
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Heat is a transfer of energy
(usually thermal energy) from a
body of higher temperature to a
body of lower temperature.
Thermal energy is the energy
associated with the random
motion of atoms and molecules.
The Law of the Conservation of Energy states that energy
can neither be created nor destroyed.
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Temperature is a
measurement of the
average kinetic energy
of the particles in a
sample of material.
Temperature is not a
form of energy.
Two temperature scales used in chemistry are Celsius and Absolute
The unit of temperature in the Celsius scale is the degree (ºC)
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The unit of temperature on the Absolute scale is the Kelvin (K)
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To convert
between
absolute and
Celsius
temperature
scales use
K=ºC+273
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Regents Question: 06/03 #41
The freezing point of bromine is
(1) 539°C
(2) –539°C
(3) 7°C
(4) –7°C
See Table S
Melting point is the same as
freezing point
Convert K to C (K=C+273)
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The concepts of kinetic and potential
energy can be used to explain
physical processes that include:
fusion (melting), solidification
(freezing), vaporization (boiling,
evaporation), condensation,
sublimation, and deposition.
Add energy
(endothermic)
subliming
melting
SOLID
Remove energy
(exothermic)
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boiling
LIQUID
freezing
GAS
condensing
depositing
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Regents Question: 06/03 #17
Which change is exothermic?
(1) freezing of water
(2) melting of iron
(3) vaporization of ethanol
(4) sublimation of iodine
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A change in phase is a change in
Potential Energy, not Kinetic Energy
Boiling Point
Melting Point
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Potential
energy changes
so temperature
doesn’t
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Energy and phase changes
 AB - solid warms up
(KE inc/PE constant)
 BC- solid melts (KE
constant/PE inc)
 CD – liquid warms
up (KE inc/PE
constant)
 DE- liquid boils (KE
constant/PE inc)
EF – gas warms (KE inc/PE constant)
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Regents Question: 06/02 #16
Which change in the temperature of a 1-gram sample of
water would cause the greatest increase in the
average kinetic energy of its molecules?
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(1) 1°C to 10°C
(3) 50°C to 60°C
(2) 10°C to 1°C
(4) 60°C to 50°C
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Heat is transferred to different
materials at different rates.
 The specific heat capacity (C) determines
the rate at which heat will be absorbed.
 The specific heat capacity for water is
4.18J/g
 The quantity of heat absorbed (Q) can be
calculated by: Q=mCT
m=mass T=change in temperature
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Regents Question: 06/02 #28
As ice melts at standard pressure, its temperature
remains at 0°C until it has completely melted. Its
potential energy
(1) decreases
(2) increases
(3) remains the same
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Regents Question: 08/02 #54
A sample of water is heated from a liquid at 40°C to a
gas at 110°C. The graph of the heating curve is
shown in your answer booklet.
a On the heating curve diagram provided in your
answer booklet, label each of the following regions:
Liquid, only
Gas, only
Phase change
Gas Only
Phase change
Liquid Only
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Regents Question: cont’d
b For section QR of the graph, state what is happening
to the water molecules as heat is added.
c For section RS of the graph, state what is happening
to the water molecules as heat is added.
They move faster, their
temperature increases.
Their intermolecular bonds are
breaking, their potential energy is
increasing.
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Regents Question: 01/02 #47
What is the melting point of this substance?
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(1) 30°C
(3) 90°C
(2) 55°C
(4) 120°C
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The quantity of energy absorbed or
released during a phase change can
be calculated using the Heat of
Fusion or Heat of Vaporization
 Melting (fusion) or freezing (solidification)
– Q=mHf where Hf is the heat of fusion
(for water: 333.6 J/g)
 Boiling (vaporization) or condensing
– Q=mHv where Hv is the heat of vaporization
(for water: 2259 J/g)
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Hf and Hv are given to Table B – m is the mass
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Regents Question: 08/02 #24
In which equation does the term “heat” represent
heat of fusion?
(1) NaCl(s) + heat  NaCl(l)
(2) NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l)+ heat
(3) H2O(l)+ heat  H2O(g)
(4) H2O(l)+ HCl(g) H3O+(aq) + Cl –(aq) + heat
Fusion refers to melting.
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Melting Point
 The temperature at which a liquid and a
solid are in equilibrium
 The melting point for ice is 0ºC
 The melting point of a substance is the same
as its freezing point
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Regents Question: 08/02 #5
Given the equation: H2O(s)
H2O(l)
At which temperature will equilibrium exist when the
atmospheric pressure is 1 atm?
(1) 0 K
(3) 273 K
(2) 100 K
(4) 373 K
K=C + 273
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Regents Question: 08/02 #18
The solid and liquid phases of water can exist in a
state of equilibrium at 1 atmosphere of pressure
and a temperature of
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(1) 0°C
(3) 273°C
(2) 100°C
(4) 373°C
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Regents Question: 06/02 #13
The strongest forces of attraction occur between
molecules of
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(1) HCl
(3) HBr
(2) HF
(4) HI
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These properties include
conductivity, malleability,
solubility, hardness, melting
point, and boiling point.
 The stronger the intermolecular forces, the
higher the boiling point and melting point.
 The stronger the intermolecular forces, the
lower the vapor pressure.
– See Table H
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A liquid will boil when its vapor
pressure equals the atmospheric
pressure.
 Raising the temperature will increase the
vapor pressure of the liquid
 Lowering the atmospheric pressure will
lower the boiling point
– On top of a high mountain, water boils at a
temperature below 100C
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Table H – the vapor pressure of four
liquids at various temperatures.
As temp inc,
vapor pressure
inc.
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Regents Question: 06/03 #40
According to Reference Table H, what is the vapor
pressure of propanone at 45°C?
(1) 22 kPa
(2) 33 kPa
(3) 70. kPa
(4) 98 kPa
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Standard pressure is 101.3 kilopascals
(kPa) or 1 atmoshpere (atm)
The normal boiling
point occurs when
the atmospheric
pressure is 101.3 kPa
(standard pressure)
The normal boiling
point of ethanol is
80ºC.
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Regents Question: 08/02 #28
As the pressure on the surface of a liquid decreases,
the temperature at which the liquid will boil
(1) decreases
(2) increases
(3) remains the same
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Regents Question: 08/02 #30
As the temperature of a liquid increases, its vapor
pressure
(1) decreases
(2) increases
(3) remains the same
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Regents Question: 08/02 #44
The vapor pressure of a liquid is 0.92 atm at
60°C. The normal boiling point of the liquid
could be
(1) 35°C
(3) 55°C
(2) 45°C
(4) 65°C
The normal boiling point is the temperature at
which a liquid boils when the atmospheric pressure
is standard pressure (1 atm or 101.3 kPa)
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Regents Question: 01/03 #68
What is the vapor pressure of liquid A at 70°C? Your
answer must include correct units. 700 mm Hg
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Regents Question: 01/03 #69
At what temperature does liquid B have the same vapor
pressure as liquid A at 70°C?
Your answer must include correct units. 113°C
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Regents Question: 01/03 #70
Which liquid will evaporate more rapidly? Explain your
answer in terms of intermolecular forces.
Liquid A will evaporate more rapidly because, at any temperature, it
has the higher vapor pressure.
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The amount of thermal energy
contained in the molecules
depends on how fast they are
moving and how many
molecules there are.
 The total kinetic energy of all the molecules
combined is called thermal energy
 Thermal energy is a result of the Kinetic Energy of
the molecules’ motion (molecules are always
moving.)
 Which can melt more ice: a small cup of hot water
or a swimming pool of cold water?
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The concept of an ideal gas is
a model to explain the
behavior of gases. A real gas
is most like an ideal gas when
the real gas is at low pressure
and high temperature.
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Kinetic molecular theory
(KMT) for an ideal gas states
that all gas particles :
 1. are in random, constant, straight-line
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motion.
 2. are separated by great distances relative to
their size; the volume of the gas particles is
considered negligible.
 3. have no attractive forces between them.
 4. have collisions that may result in the
transfer of energy between gas particles, but
the total energy of the system remains
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constant.
Real Gases
 Molecules do take up space
 Molecules do attract each other
 Energy is lost during collisions
 Under conditions of high temperature and
low pressure, real gases behave more like
ideal gases
 Hydrogen and helium are closest to being
ideal gases
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Collision theory states that a
reaction is most likely to occur
if reactant particles collide with
the proper energy and
orientation.
Anything that will increase the number of effective
collisions will increase the rate at which the reaction will
occur:
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Kinetic molecular theory
describes the relationships of
pressure, volume,
temperature, velocity, and
frequency and force of
collisions among gas
molecules.
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P1V1
P2V2
T2
T2
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Gas Laws
 Boyle’s Law
– Indirect Relationship
between pressure and
volume
– Temperature remains
constant
– PxV = constant
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 Charles’ law
– Direct relationship
between volume and
temperature
– Pressure remains
constant
– V/T = constant
– Temperature must be
Absolute temperature
(Kelvins)
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Graphing the gas laws
As absolute temperature increases,
pressure increases at constant volume
Pressure
Temperature
As absolute temperature increases,
volume increases at constant pressure
Volume
Temperature
As pressure increases, volume
decreases at constant temperature
Volume
Pressure
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Regents Question: 06/02 #14
Which graph shows the pressure-temperature
relationship expected for an ideal gas?
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Regents Question: 06/02 #15
At the same temperature and pressure, which
sample contains the same number of moles
of particles as 1 liter of O2 (g)?
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(1) 1 L Ne(g)
(3) 0.5 L SO2 (g)
(2) 2 L N2 (g)
(4) 1 L H2O(l)
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Equal volumes of different
gases at the same
temperature and pressure
contain an equal number of
particles.
Avogadro’s Hypothesis
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