Download Objectives Recognize that a system can absorb or release energy

Objectives
1.
Recognize that a system can absorb or release energy as heat in order for work to be done on
or by the system and that work done on or by a system can result in the transfer of energy as
heat.
2. Compute the amount of work done during a thermodynamic process.
3. Distinguish between isovolumetric, isothermal, and adiabatic thermodynamic processes.
Heat, Work, and Internal Energy
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______________ and ______________ are ____________ ________________________ to or
from a system. An object never has “____________” or “______________” in it; it has only
internal energy.
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A _________________ is a set of particles or interacting components considered to be a distinct
physical entity for the purpose of study.
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The _____________________________________ the combination of conditions and influences
outside a system that affect the behavior of the system.
In thermodynamic systems, work is defined in terms of _______________________ and
____________________ ________________________________
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Formula:
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This definition assumes that P is constant..
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If the gas __________________________, as shown in the figure,
V is
positive, and the work done by the gas on the piston is ___________________________.
If the gas is ________________________, V is negative, and the work done by the gas on the
piston is __________________________. (In other words, the piston does work on the gas.)
When the gas volume remains ____________________, there is no displacement and
______________________ is done on or by the system.
Although the pressure can change during a process, _________________ is done only if the
___________________ changes.
A situation in which pressure ________________________and volume remains constant is
comparable to one in which a force does not displace a mass even as the force is increased.
_____________ is not done in either situation.
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An _______________________________________________ is a thermodynamic process that
takes place at constant volume so that no work is done on or by the system.
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An ________________________________________ is a thermodynamic process that takes
place at constant temperature.
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An _______________________________________ is a thermodynamic process during which no
energy is transferred to or from the system as heat.
Thermodynamic Processes
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Section 2 The First Law of thermodynamics
Objectives
1. Illustrate how the first law of thermodynamics is a statement of energy conservation.
2. Calculate heat, work, and the change in internal energy by applying the first law of
thermodynamics.
3. Apply the first law of thermodynamics to describe cyclic processes.
Energy Conservation
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If ____________________ is taken into account,
__________________________________________________________________________
Consider the example of a roller coaster:
o A steady decrease in the car’s total mechanical energy occurs because of work
being done against the _________________________ between the car’s axles
and its bearings and between the car’s wheels and the coaster track.
o If the internal energy for the roller coaster (the system) and the energy
dissipated to the surrounding air (the environment) are taken into account, then
_________________________________________________________________
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Energy Conservation and roller coaster example
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The principle of _________________________________________________ that takes into
account a system’s internal energy as well as work and heat is called the _________________
_____________________________________.
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The first law of thermodynamics can be expressed mathematically as follows:
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Signs of Q and W for a system
Sample Problem
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The First Law of Thermodynamics
A total of 135 J of work is done on a gaseous refrigerant as it undergoes compression. If the
internal energy of the gas increases by 114 J during the process, what is the total amount of
energy transferred as heat? Has energy been added to or removed from the refrigerant as heat?
o Define
 Given:
Unknown: _______________________
 W = _______________________
 U = ______________________
Tip: Work is done on the gas, so work (W) has a negative value. The internal energy increases
during the process, so the change in internal energy (^U) has a positive value.
o Plan
Choose an equation or situation:
Apply the first law of thermodynamics using the values for U and W in order to find the value
for Q.
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Calculate
Substitute the values into the equation and solve:
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Tip: The sign for the value of Q is negative. This indicates that energy is transferred as heat from
the refrigerant.
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Evaluate
Although the internal energy of the refrigerant increases under compression, more energy is
added as work than can be accounted for by the increase in he internal energy. This energy is
removed from the gas as heat, as indicated by the minus sign preceding the value for Q.
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First Law of Thermodynamics for Special Processes
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Cyclic Processes
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A ___________________________________________ is a thermodynamic process in which a
system returns to the same conditions under which it started.
Examples include ________________________________________ and
__________________________________.
In a cyclic process, the final and initial values of internal energy are the same, and the change in
internal energy is zero.
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A __________________________________ uses heat to do mechanical work
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A heat engine is able to do work _______ by transferring energy from a high-temperature
substance (the boiler) at _______ to a substance at a lower temperature (the air around the
engine) at _________
The __________________________________________________ found in most vehicles is an
example of a heat enegine.
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Combustion Engines : The Steps of a Gasoline Engine Cycle
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Refrigeration: The Steps of a Refrigeration Cycle
 Thermodynamics of a Refrigerator
Step
Q
W
^U
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Section 3
The Second Law of Thermodynamics
Objectives

Recognize why the second law of thermodynamics requires two bodies at different
temperatures for work to be done.
 Calculate the efficiency of a heat engine.
 Relate the disorder of a system to its ability to do work or transfer energy as heat.
Efficiency of Heat Engines
 The _____________________________________________________________ can be stated as
follows:
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o No cyclic process that converts heat entirely into work is possible.
As seen in the last section,
______________________________________________________________.
According to the second law of thermodynamics, W can never be equal to Qh in a cyclic process.
In other words, some energy must always be transferred as heat to the system’s surroundings
(Qc > 0).
A measure of how well an engine operates is given by the engine’s
______________________________________________.
In general, _______________________________is a measure of the __________________
_________________ taken out of a process relative to the ________________________
___________________________ that is put into the process.
Efficiency formula
Note that efficiency is a ___________________________quantity.
Because of the second law of thermodynamics, the efficiency of a real engine is always less than
1.
Sample Problem
Heat-Engine Efficiency
Find the efficiency of a gasoline engine that, during one cycle, receives 204 J of energy from
combustion and loses 153 J as heat to the exhaust.
1. Define
Given:_____________________
____________________
Unknown: __________________
2.
Plan
Choose an equation or situation: The efficiency of a heat engine is the ratio of the work done by
the engine to the energy transferred to it as heat.
Fromula:
3.
Calculate
Substitute the values into the equation and solve:
4.
Evaluate
Only ________ percent of the energy added as heat is used by the engine to do work. As
expected, the efficiency is less than __________.
Entropy
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In thermodynamics, a system left to itself tends to go from a state with a very
____________________ set of energies to one in which there is less order.
The measure of a system’s disorder or randomness is called the _____________________of the
system. The greater the entropy of a system is, the greater the system’s disorder.
The greater probability of a disordered arrangement indicates that an _______________
______________________________________________________________________________
____________________________________________________. Put another way, the
____________________________________________________________________________
Greater _________________________ means there is less energy to do work.
If all gas particles moved __________________________ the piston, all of the internal energy
could be used to do work. This extremely well _______________________ system is highly
improbable.
Because of the connection between a system’s entropy, its ability to do work, and the direction
of energy transfer, the ____________________________________________________________
can also be expressed in terms of entropy change:
The _______________________________________________________
_____________________________________________________________________________________
______________________________.
Entropy can decrease for parts of systems, provided this decrease is offset by a greater increase in
entropy elsewhere in the universe.
Energy Changes Produced by a Refrigerator Freezing Water
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Because of the refrigerator’s less-than-perfect efficiency, the entropy of the outside air molecules
increases more than the entropy of the freezing water decreases
Describe the Entropy of the Universe
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