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thermodynamics > Chapter 2 > Flashcards

Chapter 2 Flashcards

1
Q

As a result of the conversion of electric energy consumed by the device to heat, the room temperature will ___

A

Rise

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2
Q

Total Energy E

A

The sum of thermal, mechanical, kinetic, potential, electric, magnetic, chemical and nuclear energy

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3
Q

Thermodynamics deals only with…

A

The change of the total energy

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4
Q

Those a system possesses as a whole with respect to some outside reference frame

A

Macroscopic forms of energy

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5
Q

Macroscopic forms of energy

A

Kinetic and potential energies

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6
Q

Those related to the molecular structure of a system and the degree of the molecular activity

A

Microscopic forms of energy - internal energy

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7
Q

The energy that a system possesses as a result of its motion relative to some reference from

A

Kinetic energy (KE)

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8
Q

The energy that a system possesses as a result of its elevation in a gravitational field

A

Potential Energy (PE)

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9
Q

The portion of the internal energy if a system associated with the kinetic energies of the molecules

A

Sensible energy

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10
Q

The internal energy associated with the phase of a system

A

Latent energy

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11
Q

The internal energy associated with the atomic bonds in a molecule

A

Chemical energy

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12
Q

The tremendous amount of energy associated with the strong bonds within the nucleus of the atom itself

A

Nuclear energy

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13
Q

Thermal

A

Sensible + latent

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14
Q

Internal

A

Sensible + latent + chemical + nuclear

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15
Q

The total energy of a system, can be contained or stored in a system, and thus can be viewed as the

A

Static forms of energy

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16
Q

The forms of energy not stored in a system can be viewed as the

A

Dynamic forms of energy or as energy interactions

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17
Q

Dynamic forms of energy

A

Recognized at the system boundary as they cross it, and they represent the energy gained or lost by a system during a process

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18
Q

The only two forms of energy interactions associated with a closed system are

A

Heat transfer and work

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19
Q

The difference between heat transfer and work

A

An energy interaction is heat transfer if its driving force is a temperature difference. Otherwise it is work.

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20
Q

The form of energy that can be converted to mechanical work completely and directly by an ideal mechanical device such as an ideal turbine

A

Mechanical energy

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21
Q

The familiar forms of mechanical energy

A

Kinetic and potential energies

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22
Q

The form of energy that is transferred between two systems (or a system and its surroundings) by virtue of a temperature difference

A

Heat

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23
Q

Temperature difference is the driving force for ____

A

Heat transfer

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24
Q

Energy is recognized as heat transfer only as it…

A

Crosses the system boundary

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25
Q

Treats molecules as tiny balls that are in motion and thus possess kinetic energy

A

Kinetic theory

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26
Q

The energy associated with the random motion of atoms and molecules

A

Heat

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27
Q

The transfer of energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interaction between particles

A

Conduction

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28
Q

The transfer of energy between a solid surface and the adjacent fluid that is in motion, and it involves the combined effects of conduction and fluid motion

A

Convection

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29
Q

The transfer of energy due to the emission of electromagnetic waves (or photons)

A

Radiation

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30
Q

Heat was thought to be an invisible fluid called the _____ that flowed from warmer bodies to the cooler ones

A

Caloric

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31
Q

The energy transfer associated with a force acting through a distance

A

Work

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32
Q

Work interactions

A

A rising piston, a rotating shaft, and an electric wire crossing the system boundaries

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33
Q

Formal sign convention

A

Heat transfer to a system (Qin) and work done by a system (Wout) are positive

Heat transfer to a system (Qout) and work done on a system (Win) are negative

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34
Q

Both heat and work are _____

A

Boundary phenomena - recognized at the boundaries of a system as they cross the boundaries

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35
Q

Systems posses ___

A

Energy but not heat or work

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36
Q

Heat vs. work

A

Both are associated with a process not a state

Has no meaning at a state

Both are path functions

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37
Q

Path functions

A

Their magnitudes depend on the path followed during a process as well as the end states

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38
Q

Properties are ___

A

Point functions

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39
Q

There are two requirements for a work interaction between a system and its surrounds to exist

A

There must be a force acting on the boundary

The boundary must move

40
Q

Work done to raise or to accelerate a body

A
  1. The work transfer needed to raise a body is equal to the change in the potential energy of the body
  2. The work transfer needed to accelerate a body is equal to the change in the kinetic energy of the body
41
Q

Nonmechanical forms of work

A

Electrical work
Magnetic work
Electrical polarization work

42
Q

Electrical work

A

Generalized force - voltage (electrical potential)

Generalized displacement - electrical charge

43
Q

Magnetic work

A

Generalized force - magnetic field strength

Generalized displacement - magnetic dipole moment

44
Q

Electrical polarization work

A

Generalized force - electric field strength

Generalized displacement - polarization of the medium

45
Q

Provides a sound basis for studying the relationships among the various forms of energy and energy interactions

A

The first law of thermodynamics (the conversation of energy principle)

46
Q

The first law of thermodynamics

A

Energy can be neither created nor destroyed during a process; it can only change forms

47
Q

Energy balance

A

(Total energy entering the system) - (total energy leaving the system) = (change in the total energy of the system)

48
Q

Energy change of a system

A

Energy change = energy at final state - energy at initial state

49
Q

Net energy transfer by heat, work, and mass

A

Ein- Eout

50
Q

Change in internal, kinetic, potential, etc. energies

A

Change in Esystem

51
Q

Mechanisms of energy transfer

A

Heat transfer
Work transfer
Mass flow

52
Q

A closed mass involves only

A

Heat transfer and work

53
Q

Is one of the most frequently used terms in thermodynamics, and it indicates how well an energy conversion or transfer process is accomplished

A

Efficiency

54
Q

The amount of heat released when a unit amount of fuel at room temperature is completely burned and the combustion products are cooled to the room temperature

A

Heating value of the fuel

55
Q

Lower heating value (LHV)

A

When the water leaves as a vapor

56
Q

Higher heating value (HHV)

A

When the water in the combustion gases is completely condensed and thus the heat of vaporization is also recovered

57
Q

A device that converts mechanical energy to electrical energy

A

Generator

58
Q

The ratio of the electrical power output to the mechanical power input

A

Generator efficiency

59
Q

The ratio of the net electrical power output to the rate of fuel energy input

A

Thermal efficiency of a power plant

60
Q

The amount of light output in lumens per W of electricity consumed

A

Lighting efficacy

61
Q

Using energy-efficient appliances ___

A

Conserve energy

62
Q

The combustion of fuel produces

A

Carbon dioxide (global warming)
Nitrogen oxides and hydrocarbons (smog)
Carbon monoxide
Sulfur dioxide (acid rain)

63
Q

The effectiveness of the conversion process between the mechanical work supplied or extracted and the mechanical energy of the fluid is expressed by the

A

Pump efficiency and turbine efficiency

64
Q

There are 3 modes of heat transfer:

A

Conduction
Convection
Radiation

65
Q

All modes require temperature difference between

A

Source and sink

66
Q

Heat transfers how?

A

From high temperature to low temperature

67
Q

Transfer of more energetic particles to less energetic particles

A

Conduction

68
Q

Occurs in solids, liquids, and gasses

A

Conduction

69
Q

Conduction: liquids and gasses

A

Collision of molecules during random motion (Brownian motion)

70
Q

Conduction: solids

A

Combination of crystal lattice vibrations and energy transport by free electrons

71
Q

Heat of conduction is proportional to…

A

Temperature difference and area normal to heat transfer

72
Q

Proportionality constant measures material’s ability to conduct heat

A

Thermal conductivity

73
Q

High k

A

Conductors (most metals)

74
Q

Low k

A

Insulators (wood, styrofoam)

75
Q

Fourier’s law of heat conduction

A

Negative sign is used to due to negative temperature

76
Q

Transfer of energy to/from a solid surface from/to an adjacent moving fluid (liquid or gas)

A

Convection

77
Q

Combination of conduction and fluid motion

A

Convection

78
Q

____ fluid motion results in more heat transfer

A

Faster

79
Q

If fluid is motionless

A

Pure conduction occurs

80
Q

Fluid is forced over surface by external means (fan, pump, wind, etc.)

A

Forced convection

81
Q

Fluid motion is caused by buoyancy force due to changes in density (warmer air rises because it is less dense)

A

Free (or natural) convection

82
Q

Heat transfer in processes that involve phase changes in fluids are considered to be

A

Convection - evaporation, condensation

83
Q

Movement of vapor bubbles through a liquid

A

Evaporation

84
Q

Falling of liquid droplets

A

Condensation

85
Q

Convective heat transfer coefficient

A

Not a property of the fluid

Determined experimentally; affected by surface geometry, fluid properties, fluid velocity

86
Q

Ts

A

Surface temperature

Temp of fluid at surface

87
Q

Tf

A

Bulk fluid

88
Q

Radiation

A

Energy is emitted by matter in the form of electromagnetic waves (or photons)

89
Q

Results from the change of electronic configurations of atoms or molecules

A

Radiation

90
Q

Does not require presence of medium between source and sink; can work in a vacuum

A

Radiation

91
Q

All bodies at a temperature above ____ emit thermal radiation

A

Absolute zero

92
Q

Maximum radiation from a surface

A

Stefan-Boltzman’s Law

93
Q

Surface that emits maximum radiation is called a

A

Black body

94
Q

___ surfaces emit less than the maximum

A

Real

95
Q

Emissivity

A

Material property between 0 and 1

1 for blackbodies

96
Q

Pollutants emitted during the combustion of fossil fuels are responsible for

A

Smog, acid rain, global warming

97
Q

The environmental pollution has reached such high levels that it became a serious threat to

A

Vegetation, wild life, human health

thermodynamics (11 decks)

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