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OPEN SYSTEM
A system that can exchange both mass and energy
with its surroundings.
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OPEN SYSTEM
A system that can exchange both mass and energy
with its surroundings.
CLOSED SYSTEM
A system that allows energy but not mass transfer
with its surroundings.
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OPEN SYSTEM
A system that can exchange both mass and energy
with its surroundings.
CLOSED SYSTEM
A system that allows energy but not mass transfer
with its surroundings.
ISOLATED SYSTEM
A system that does not allow energy or mass
transfer with its surroundings.
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STATE OF A SYSTEM
The macroscopic variables such as composition,
volume, pressure, temperature, etc., that define a
particular system.
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STATE OF A SYSTEM
The macroscopic variables such as composition,
volume, pressure, temperature, etc., that define a
particular system.
STATE FUNCTION
Any property of a system that is fixed by the state
the system is in. (A change in a state function is
independent of the path followed – it depends only
on the initial and final states of the system.)
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Example of a state function: If we have 1 mole of a
gas at a given temperature and pressure – then the
volume can’t be varied, its fixed by the state of the
system defined by the variables n, T, and p. V can be
calculated from
V  nRT
p
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Example of a state function: If we have 1 mole of a
gas at a given temperature and pressure – then the
volume can’t be varied, its fixed by the state of the
system defined by the variables n, T, and p. V can be
calculated from
V  nRT
p
The important property of a state function is that a
change in a state function is independent of the
path followed by the system – only the initial and
final values are needed to calculate the change.
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The First Law of Thermodynamics
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The First Law of Thermodynamics
The First Law of Thermodynamics: The energy of
the universe is constant.
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The First Law of Thermodynamics
The First Law of Thermodynamics: The energy of
the universe is constant.
Mass-energy statement: The sum of all the mass
and all the energy in the universe is constant.
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The First Law of Thermodynamics
The First Law of Thermodynamics: The energy of
the universe is constant.
Mass-energy statement: The sum of all the mass
and all the energy in the universe is constant.
The first law of thermodynamics describes
conservation of energy.
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The first law of thermodynamics is sometimes
expressed as: The energy change in any system is
equal to the heat absorbed by the system plus the
work done on the system. This is a particularly
useful statement for the purposes of doing
calculations.
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The first law of thermodynamics is sometimes
expressed as: The energy change in any system is
equal to the heat absorbed by the system plus the
work done on the system. This is a particularly
useful statement for the purposes of doing
calculations.
Recall that delta, Δ , denotes “change in”, so ΔX
denotes ΔX  Xfinal  Xinitial.
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The first law of thermodynamics is:
ΔE  q  w
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The first law of thermodynamics is:
ΔE  q  w
where ΔE is the change in the internal energy,
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The first law of thermodynamics is:
ΔE  q  w
where ΔE is the change in the internal energy,
w is the work done on the system
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The first law of thermodynamics is:
ΔE  q  w
where ΔE is the change in the internal energy,
w is the work done on the system
q is the heat absorbed by the system
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The first law of thermodynamics is:
ΔE  q  w
where ΔE is the change in the internal energy,
w is the work done on the system
q is the heat absorbed by the system
The work w can be expressed in terms of two
different types of work: the work of expansion, and
non-expansion work:
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The first law of thermodynamics is:
ΔE  q  w
where ΔE is the change in the internal energy,
w is the work done on the system
q is the heat absorbed by the system
The work w can be expressed in terms of two
different types of work: the work of expansion, and
non-expansion work:
w  wexp  wnon -exp
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The first law of thermodynamics is:
ΔE  q  w
where ΔE is the change in the internal energy,
w is the work done on the system
q is the heat absorbed by the system
The work w can be expressed in terms of two
different types of work: the work of expansion, and
non-expansion work:
w  wexp  wnon -exp
Expansion work involves a volume change, nonexpansion work does not.
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Expansion work
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ΔE  Efinal  Einitial
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A system transferring energy as heat only.
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A system transferring energy as work only.
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Sign Convention
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Sign Convention
Work
w is positive if work is done on the system
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Sign Convention
Work
w is positive if work is done on the system
w is negative if work is done (by the system) on the
surroundings
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Sign Convention
Work
w is positive if work is done on the system
w is negative if work is done (by the system) on the
surroundings
Heat
q is positive if heat is added to the system
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Sign Convention
Work
w is positive if work is done on the system
w is negative if work is done (by the system) on the
surroundings
Heat
q is positive if heat is added to the system
q is negative if heat is added (by the system) to the
surroundings
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Sign Convention
Work
w is positive if work is done on the system
w is negative if work is done (by the system) on the
surroundings
Heat
q is positive if heat is added to the system
q is negative if heat is added (by the system) to the
surroundings
Summary: To the system is positive,
To the surroundings is negative.
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The following simple example uses the First Law of
Thermodynamics and we pay attention to the sign
convention.
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The following simple example uses the First Law of
Thermodynamics and we pay attention to the sign
convention.
Example: The work done in compressing a gas in a
cylinder is 299 J. During the process, there is a heat
transfer of 70.3 J from the gas to the surroundings.
Calculate the change in the internal energy of the
gas.
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The following simple example uses the First Law of
Thermodynamics and we pay attention to the sign
convention.
Example: The work done in compressing a gas in a
cylinder is 299 J. During the process, there is a heat
transfer of 70.3 J from the gas to the surroundings.
Calculate the change in the internal energy of the
gas.
The gas is the system in this problem.
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The following simple example uses the First Law of
Thermodynamics and we pay attention to the sign
convention.
Example: The work done in compressing a gas in a
cylinder is 299 J. During the process, there is a heat
transfer of 70.3 J from the gas to the surroundings.
Calculate the change in the internal energy of the
gas.
The gas is the system in this problem.
ΔE  q  w
= -70.3 J + 299 J
= 229 J.
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Entropy and The Second Law of
Thermodynamics
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Entropy and The Second Law of
Thermodynamics
Exothermic reactions (ΔH is negative) indicate that
energy is given off to the surroundings and so the
products of the reaction have a lower energy than
the reactants.
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Entropy and The Second Law of
Thermodynamics
Exothermic reactions (ΔH is negative) indicate that
energy is given off to the surroundings and so the
products of the reaction have a lower energy than
the reactants.
First impression: might expect that the sign of ΔH
tells which direction a reaction (or process) will go.
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Entropy and The Second Law of
Thermodynamics
Exothermic reactions (ΔH is negative) indicate that
energy is given off to the surroundings and so the
products of the reaction have a lower energy than
the reactants.
First impression: might expect that the sign of ΔH
tells which direction a reaction (or process) will go.
This turns out not to be the case. The melting of ice
is a counter example.
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Key question: How do we tell which reactions
(or processes) proceed in the forward direction?
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Spontaneous Processes
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Spontaneous Processes
Spontaneous Process: A process that can occur by
itself, without the input of energy from the
surroundings.
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Spontaneous Processes
Spontaneous Process: A process that can occur by
itself, without the input of energy from the
surroundings.
It is logical to assume that spontaneous processes
occur so as to decrease the energy of the system.
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Spontaneous Processes
Spontaneous Process: A process that can occur by
itself, without the input of energy from the
surroundings.
It is logical to assume that spontaneous processes
occur so as to decrease the energy of the system.
There are many spontaneous processes that
cannot be understood by considering energy
changes alone.
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Example of a spontaneous process: the
expansion of a gas into a vacuum.
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We can design the experiment so that there is no
exchange of energy between the system and the
surroundings during the expansion.
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We can design the experiment so that there is no
exchange of energy between the system and the
surroundings during the expansion.
Therefore, factors other than the energy must be
responsible for this occurrence.
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We can design the experiment so that there is no
exchange of energy between the system and the
surroundings during the expansion.
Therefore, factors other than the energy must be
responsible for this occurrence.
The clue is found when we realize that before the
expansion, all the molecules are in one container.
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We can design the experiment so that there is no
exchange of energy between the system and the
surroundings during the expansion.
Therefore, factors other than the energy must be
responsible for this occurrence.
The clue is found when we realize that before the
expansion, all the molecules are in one container.
Because they are confined in a smaller volume, the
system is more ordered (less random) than it is
after expansion.
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This is a general principle: Spontaneous processes
tend to occur when there is an increase of disorder
or randomness of the universe.
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This is a general principle: Spontaneous processes
tend to occur when there is an increase of disorder
or randomness of the universe.
The thermodynamic quantity used as a measure of
the disorder or randomness of a system is called the
entropy. (Clausius, 1865: from Greek:
transformation (lit. ‘turning’)).
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This is a general principle: Spontaneous processes
tend to occur when there is an increase of disorder
or randomness of the universe.
The thermodynamic quantity used as a measure of
the disorder or randomness of a system is called the
entropy. (Clausius, 1865: from Greek:
transformation (lit. ‘turning’)).
Symbol used for entropy: S
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This is a general principle: Spontaneous processes
tend to occur when there is an increase of disorder
or randomness of the universe.
The thermodynamic quantity used as a measure of
the disorder or randomness of a system is called the
entropy. (Clausius, 1865: from Greek:
transformation (lit. ‘turning’)).
Symbol used for entropy: S
The units for S are: J K-1
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This is a general principle: Spontaneous processes
tend to occur when there is an increase of disorder
or randomness of the universe.
The thermodynamic quantity used as a measure of
the disorder or randomness of a system is called the
entropy. (Clausius, 1865: from Greek:
transformation (lit. ‘turning’)).
Symbol used for entropy: S
The units for S are: J K-1
The units for molar entropies are: J K-1 mol-1
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Entropy and the number of
microstates
Each quantized state of a whole system of
molecules is called a microstate. The number of
microstates for a system is the number of ways the
system can disperse its energy among the various
modes of motion of all its molecules. This number is
designated by W.
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