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ME 100 > Topic 2 > Flashcards

Topic 2 Flashcards

Energy and the First Law of Thermodynamics

1
Q

Kinetic energy is

A

Scalar Quantity

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2
Q

What is an extensive property?

A

An extensive property is one that depends on the amount of matter in a system or the size of the system

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3
Q

Why is kinetic energy an extensive property?

A

it changes in proportion to the amount of matter in a system

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4
Q

What is the difference between a scalar and a vector quantity?

A

A scalar quantity has only magnitude, but no direction. Vector quantity has both magnitude and direction

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5
Q

Why is potential energy also considered an extensive property?

A

Because it depends on the amount of matter in the system—in other words, it scales with the size or quantity of the system.

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6
Q

Work is equal to

A

Force (distance)

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7
Q

Conversation of Energy

A

states that the total work of all forces acting on the body from the surroundings, with the exception of the gravitational force, equals the sum of the changes in the kinetic and potential energies of the body.

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8
Q

Thermodynamic definition of work

A

“Work is done by a system on its surroundings if the sole effect
on everything external to the system could have been the
raising of a weight.

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9
Q

W > 0

A

positive (+)

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10
Q

W < 0:

A

negative (-)

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11
Q

work done BY the system

A

positive (+)

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12
Q

work done ON the system

A

negative (-)

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13
Q

The rate of energy transfer by work

A

Power

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14
Q

is one in which the departure from thermodynamic equilibrium is at most infinitesimal.

A

quasiequilibrium process (or quasistatic) process

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15
Q

a change that a gas undergoes under general conditions

A

Polytropic Process

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16
Q

When n = 0 in a polytropic process

A

process is an isobaric (constant-pressure) process

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17
Q

When n = +- infinity in a polytropic process

A

process is an isometric (constant-volume) process

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18
Q

For ideal gas n = 1 in a polytropic process

A

isothermal (constant-temperature) process

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19
Q

Internal energy is what property

A

extensive property of the system

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20
Q

amount of energy transferred across the boundary of a system in a heat interaction with the system’s surroundings.

A

Heat

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21
Q

Q > 0

A

positive (+)

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22
Q

Q < 0

A

negative (-)

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23
Q

heat transfer from the system

A

negative (-)

24
Q

heat transfer to the system

A

positive (+)

25
Q

Work and Heat is a property?

A

Both are not a property

26
Q

lowercase delta (δ)

A

denotes an infinitesimal or differential amount of heat added to or removed from a system. This symbol highlights that heat (𝑄) is a path-dependent quantity, meaning it depends on the specific path taken during a process rather than the end states alone.

27
Q

units for heat transfer Q and heat transfer rate Q (.)

A

same as those introduced
previously for W and W (.) respectively.

27
Q

adiabatic

A

means without heat transfer.

28
Q

if a system undergoes a process involving no heat transfer with its surroundings

A

adiabatic process

29
Q

Heat Transfer Modes

A

Three basic transfer mechanisms:
1. Conduction
2. Convection
3. Thermal radiation

30
Q

Energy transfer can take place in solids, liquids, and gases.

A

Conduction

31
Q

Transfer of energy from the more energetic particles of a substance to adjacent particles that are less energetic due to interactions between particles.

A

Conduction

32
Q

rate of heat transfer across
any plane normal to the x direction, Qx, is proportional to the wall area, A, and the temperature gradient in the x direction, dT/dx:

A

Fourier’s law

33
Q

the negative gradient of temperature and the time rate of heat transfer is proportional to the area at right angles of that gradient through which the heat flows

A

Fourier’s law

34
Q

Fourier’s law is also known as

A

law of heat conduction

35
Q

Substances with large values of thermal conductivity

A

good conductors

36
Q

Substances with small values of thermal conductivity

A

good insulators

37
Q

is emitted by matter as a result of changes in the electronic configurations of the atoms or molecules within it.

A

Thermal radiation

38
Q

The energy is transported by

A

electromagnetic waves (or photons)

39
Q

requires no intervening medium

A

thermal radiation

40
Q

Stefan–Boltzmann law

A

shows that the thermal radiation is associated with the fourth power of the absolute temperature of the surface, Tb

41
Q

Stefan–Boltzmann law states that

A

the magnitude of the radiation output of an object is directly proportional to the fourth power of its surface temperature

42
Q

property of the surface that indicates how effectively the surface radiates (0≤ ε ≤ 1.0)

A

Emissivity (ε)

43
Q

Stefan– Boltzmann constant (σ )

A

5.67 x 10^-8 W/m^2 K^4

44
Q

Stefan– Boltzmann constant (σ )

A

0.1714 x 10^-8 Btu/h . ft^2°R^4

45
Q

energy transfer between a solid surface

A

Convection

46
Q

adjacent gas or liquid at another temperature

A

Convection

47
Q

heat transfer coefficient

A

not a thermodynamic property

48
Q

Similarities of Heat and Work

A
  • both transient phenomena
  • Systems never possess heat or work, but either or both cross
  • boundary phenomena
  • Both are observed only at the boundary of the system, and both represent energy crossing the boundary
  • Both heat and work are path functions and inexact differentials.
49
Q

What is Transient

A

the evaluation of how a system responds to fixed and varying boundary conditions over time

50
Q

APPLICATION of the conservation of energy principle to heat and thermodynamic

A

First law of themodynamics

51
Q

The change in internal energy of a system is equal to the heat added to the system minus the work done by the system

A

Energy Balance for Closed Systems

52
Q

Energy balance in differential form

A

dE = δQ (.) - W (.)

53
Q

The instantaneous time rate form of the energy
balance is

A

dE/dt = Q (.) - W (.)

54
Q

Rate form of the energy balance

A

Time rate of change of the energy contained within the system at time t

=

Net rate at which energy is being transferred in by heat transfer at time t

-

Net rate at which energy is being transferred out by work at time t

ME 100 (5 decks)

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