thermodynamics
DESCRIPTION
Heat and Thermodynamic process, phase change, carnot engine, entropyTRANSCRIPT
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ThermodynamicsHeat and Temperature, Thermal
Properties of Matter, The First Law of Thermodynamics, The Second Law of
Thermodynamics, Heat Engines, Internal-Combustion Engines,
Refrigerators, Carnot Cycle, Entropy
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Physics vocabulary
• It is a thermodynamics process with no heat transfer into or out of the system.
• Adiabatic• What is a constant-
temperature thermodynamic process?
• Isothermal• What is a thermodynamic
process at constant atmospheric pressure?
• Isobaric• It is a constant-volume
thermodynamic process• Isochoric
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Example
• A surveyor uses a steel measuring tape that is exactly 50.000m long at a temperature of 20°C. What is its length on a hot summer day when the temperature is 35°C? α= 1.2 x10-
3/C°
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Example
• Feed a cold, starve a fever: During a bout with the flu, an 80-kg man ran a fever of 2.0°C above normal, that is a body temperature of 39.0°C. Assuming that the body is mostly water, how much heat is required to raise his temperature by that amount? cwater= 4190J/KgK
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TEMPERATURE AND HEAT
Thermal Equilibrium, Temperature Scales, Thermal Expansion, Quantity of Heat, Calorimetry and Phase Changes, Mechanisms of Heat transfer
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Temperature and Thermal Equilibrium
• Temperature is a measure of hotness or coldness.
• When an interaction causes no further change in the system, then it is in the state of thermal equilibrium.
• Two systems are in thermal equilibrium if and only if they have the same temperature.
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Zeroth Law of thermodynamics
If one system is initially in thermal equilibrium with two other
systems, then, these two other systems are also in thermal
equilibrium with each other.
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Thermometric Scales
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Thermal Expansion
Linear expansion
Volume expansion
Thermal Stress
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Quantity of Heat (Q)
Energy transfer that takes place solely because of temperature difference is called
heat flow or heat transfer, and energy transferred in this way is called heat.
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Quantity of Heat (Q)
Calorie (cal) is defined as the amount of heat required to raise the temperature of one gram of water from 14.5°C- 15.5°C
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Conversion factors for the Quantity of Heat
1 cal = 4.186J1 kcal =1000 cal = 4186 J 1 Btu= 778 ft.lb = 252 cal = 1055 J
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Specific Heat Capacity (C)
The amount of heat needed to raise one kilogram of a substance to 1C°
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Phase Changes
• The term phase is used to describe the specific state of matter.• A transition from one phase to
another is called a phase change or phase transition.
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Phase Change
• Heat of fusion (Lf)- the heat required per unit mass in changing solid to liquid
• Heat of vaporization (Lv)- the heat required per unit mass in changing liquid to gas
• Heat of combustion (Lc) - the heat required per unit mass in complete combustion of one gram of gasoline
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Phase Change
Solid Liquid GasLf Lv
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Mechanisms of Heat transfer
• Conduction occurs between a body or between two bodies in contact.• Convection depends on motion of
mass from one region of space to another.• Radiation is heat transfer by EM
radiation
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Example
• A surveyor uses a steel measuring tape that is exactly 50.000m long at a temperature of 20°C. What is its length on a hot summer day when the temperature is 35°C? α= 1.2 x10-
3/C°
• 50.009m
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Example
• Feed a cold, starve a fever: During a bout with the flu, an 80-kg man ran a fever of 2.0°C above normal, that is a body temperature of 39.0°C. Assuming that the body is mostly water, how much heat is required to raise his temperature by that amount? cwater= 4190J/Kg.K
• 6.7x105J= 133kcal
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THERMAL PROPERTIES OF MATTER
Molecular Properties of Matter, KMT, Heat Capacities, Phases of Matter
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KMT1. Gases are considered to be
composed of minute discrete particles.
2. The molecule in a container are believed to be in ceaseless motion during which they collide with each other and the walls of the container
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KMT3. The molecular collision is perfectly
elastic.4. The molecules average KE is
proportional to any given absolute temperature.
5. All forces of attraction are negligible due to rapid molecular separation.
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Gas Laws
• Boyle’s Law:P1 x V1 = P2 x V2
• Charles’ Law: V1/T1 = V2/T2
• Gay-Lussac’s Law: P1/T1 = P2/T2
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Ideal Gas law
Emphasizes on the amount of substance and its effect on the
volume of a gas, represented by Avogadro’s law
n α V if PV α RT, then PVα nRT
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Graham’s law of diffusion
The rate of flow of a gas molecule is inversely proportional to the square root of its density or its molecular weight, at constant temperature and
pressure.
r1/r2 = √ (d2/d1)
r1/r2 = √ (MW2/MW1)
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Example
• How much faster does H2 travel than O2 molecule at the same temperature and pressure if molecular weights of H2 and O2 are 2g/mole and 32g/mole respectively?• H2 molecules travel 4times
faster than O2 molecules
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Root-mean-square speed of a gas molecule
Where k is the ratio of R to NA (Boltzman constant)= 1.381x10-23 J/molecule.K
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FIRST LAW OF THERMODYNAMICS
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Water is heated, then boils;the expanding steam does work
to propel the locomotive
Explain the thermodynamic process
in making popcorn
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First Law of Thermodynamics
Internal energy is the change in initial and final energies of the system
Internal energy is the sum of heat exchange between the system and the surroundings and W done on or by the systemUsed in
some sources
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Sign Convention
• W done on the system: +• W done by the system: -• Heat added to the system: +• Heat released by the system: -
Used in some
sources
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First Law of Thermodynamics
Internal energy is the change in initial and final energies of the system
Internal energy is the sum of heat exchange between the system and the surroundings and W done on or by the system
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Sign Convention
• W done on the system: -• W done by the system: +• Heat added to the system: +• Heat released by the system: -
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Adiabatic Process
Q=0 U2-U1= -W
no heat transfer into or out of the system
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Isochoric Process
W= 0 U2-U1= Q
it does no work
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Isobaric Process
W,Q,∆U≠0
p(V2-V1 )= W
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Isothermal Process
W,Q,∆U≠0
Q = WIf ∆U=0 (Ideal gas)
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SECOND LAW OF THERMODYNAMICS
Heat engines, Internal-Combustion Engines, Refrigerators, Carnot Cycle, Entropy
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Explain the thermodynamic process
in this picture
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Second Law of Thermodynamics
a general principle which places constraints upon the direction
of heat transfer and the attainable efficiencies of heat engines
In so doing, it goes beyond the limitations imposed by the first law of thermodynamics.
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Second Law of Thermodynamics: heat engines
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Second Law of Thermodynamics: heat
enginesThe most efficient heat engine cycle is the Carnot
cycle, consisting of two isothermal processes and two adiabatic processes.
the Carnot efficiency: the processes involved in the
heat engine cycle must be reversible and
involve no change in entropy
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Carnot Engine
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The 4-stroke engine cycle
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The 4-stroke engine cycle
• Intake stroke: the inlet valve is open and a fresh fuel-air mixture is pulled into the cylinder by the downward motion of the piston.
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The 4-stroke engine cycle
• Compression stroke: the piston moves upward, compressing the mixture. The temperature and pressure increase. Prior to the piston reaching the top of its travel, the spark plug ignites the mixture and a flame begins to propagate across the combustion chamber.
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The 4-stroke engine cycle
• Expansion/Power stroke: the flame continues its travel across the combustion chamber. The high pressure in the cylinder pushes the piston downward. Energy is extracted from the burned gases in the process.
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The 4-stroke engine cycle
• Exhaust stroke: the hot products flow rapidly out of the cylinder because of the relatively high pressure within the cylinder compared to that in the exhaust port.
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Second Law of Thermodynamics:
RefrigeratorsIt is not possible for heat to flow from a colder body to a warmer body
without any work having been done to accomplish this flow.
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Second Law of Thermodynamics:
RefrigeratorsEnergy will not flow spontaneously
from a lower temperature object to a higher temperature object.
“second form” or Clausius Statement
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Second Law of Thermodynamics: Refrigerators
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2 vs 7
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Second Law of Thermodynamics: Entropy
• In any cyclic process the entropy will either increase or remain the same.
• Entropy is a measure of the amount of energy which is unavailable to do work.
• Entropy is a measure of the multiplicity of a system.
• Entropy is a measure of the disorder of a system.
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/seclaw.html