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PHSI > Module 3: Thermodynamics > Flashcards

Module 3: Thermodynamics Flashcards

1
Q

Minimum value of Kelvins

A

0K

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2
Q

How can temperature be changed?

A

By transfer of thermal energy

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3
Q

How can a constant-volume gas thermometer be used?

A

By comparing with a triple point cell

T/Ttp = P/Ptp

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4
Q

Secondary thermometers and how they are made accurate

A

One which is practical for general use

Calibrated against a primary thermometer

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5
Q

Thermal energy

A

Energy of matter due to the vibration (and translational motion- just gas) of molecules

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6
Q

When two non-identical objects are joined, which property is made equal?

A

Temperature (not thermal energy)

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7
Q

Heat transfer

A

Movement of thermal energy

Higher nervy molecules share energy with lower energy molecules

Occurs until thermal equilibrium is reached

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8
Q

Thermal equilibrium

A

When both objects are the same temperature

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9
Q

Why does thermal expansion occur?

A

Molecules move further apart as they start moving faster due to increase in temperature. This causes expansion of the object

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10
Q

α (thermodynamics)

A

Expansion coefficient

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11
Q

What are the expansion coefficients of 2D and 3D objects?

A

2α and 3α

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12
Q

Ideal gases all have the same ____?

A

Volume expansion coefficient

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13
Q

Why do ideal gases have the same volume expansion coefficient? (2)

A

Volume of atoms/ molecules is very small compared to the volume available

Atoms/ molecules don’t stick together

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14
Q

What is the relationship between number of particles and volume when pressure is increased?

A

The more particles, the greater the increase in volume

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15
Q

Which two laws contribute to the ideal gas law?

A

Charles’ law and Boyle’s law

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16
Q

What does N stand for in the ideal gas law PV = NkT ?

A

Total number of atoms/ molecules

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17
Q

What does k stand for in the ideal gas law PV = NkT ?

A

Boltzmann constant

1.38 x 10^-23 J K^-1

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18
Q

n = N/?

A

NA (Avogadros constant)

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19
Q

Does the ideal gas law apply to pure gases or mixtures?

A

Both

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20
Q

Dalton’s law

A

P = P1 + P2

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21
Q

ppm

A

Parts per million

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22
Q

Partial pressure

A

The pressure one gas contributes to the total pressure in a mixture

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23
Q

Temperature is a measure of (apart from heat)?

A

Average kinetic energy per atom/ molecule

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24
Q

________

1/2mv^2

A

Average kinetic energy per molecule

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25
Q

U (thermodynamics)

A

Total kinetic energy

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26
Q

What does the Maxwell-Boltzmann distribution show?

A

The molecules of a gas have a wide range of speeds

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27
Q

What is the most common speed for O2 gas molecules?

A

400ms^-1

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28
Q

For real gases, when does the ideal gas relationship fail?

A

When T is low enough

Or V is small enough

29
Q

What happens when T or V is low enough for a real gas?

A

Attractive forces between atoms of the gas cause them to stick together

Gas condenses into a liquid or solid

Called a phase change

30
Q

Does T change when phase changes?

A

No

31
Q

Saturated vapour pressure

A

The pressure at which a substance can co-exist as a liquid and vapour at a certain temperature

32
Q

Does each substance have more than one vapour pressure?

A

Yes- at different temperatures

33
Q

How can we boil water at room temperature?

A

Decrease the pressure

34
Q

Why is thermal energy needed for phase change?

A

To overcome inter-atomic forces

35
Q

Q (thermodynamics)

A

Thermal energy input

36
Q

L (thermodynamics)

A

Latent heat: the thermal energy required for 1kg of a substance to melt or vapourise

At a specific temperature

37
Q

kWh

A

Kilowatt hour

Equal to 3.6MJ

38
Q

First law of thermodynamics

A

Energy of an isolated system is constant

39
Q

Q = mcdT

A

Q thermal energy input
m mass
c specific heat capacity
dT change in temperature

40
Q

Specific heat capacity

A

(c) amount of heat required to raise temperature of 1kg of a substance by 1K (or 1 degree Celsius)

41
Q

Dew-point temperature

A

The temperature at which a certain (partial) pressure of water starts to condense/ form dew

42
Q

Is the partial pressure of water vapour usually more or less than the saturated vapour pressure?

When are they equal?

A

Less- the saturated vapour pressure is the max amount a volume can hold

It is equal to the saturated vapour pressure of water of a lower temperature

43
Q

Moisture content in the air

A

The mass of moisture per kg of dry air

44
Q

Dry air

A

Air in our atmosphere containing nitrogen oxygen etc.

45
Q

Other names for moisture content (2)

A

Absolute humidity

Humidity ratio

46
Q

mw/ma

A

Humidity ratio

Mass of water / mass of air

47
Q

Dry-bulb temperature

A

Normal air temperature

48
Q

Relative humidity

A

Partial water vapour pressure/ saturated vapour pressure at same T

(Percentage humidity of what is possible)

49
Q

If given dew-point T and dry-bulb T

How do you find the relative humidity in a psychometric chart?

A

Dew-point is at 100% relative humidity- so find the moisture content that corresponds with this data point

Find the data point that connects the moisture content to the dry-bulb temperature

Find the RH line closest to second point

50
Q

Wet-bulb temperature

A

The equilibrium temperature at which the rate of heat lost by the wet bulb is equal to the rate of heat gained from the surroundings

Basically how cool a wet cloth over a thermometer can become

51
Q

When does wet-bulb temperature = dry-bulb temperature?

A

When RH= 100%

52
Q

Three forms of heat transfer

A

Conduction
Convection
Radiation

53
Q

dQ/dt

A

Rate of heat transfer

54
Q

h conduct

A

Conduction heat transfer coefficient

h cond= k/d

Where d = thickness

55
Q

What is k in thermodynamics?

A

Thermal conductivity

56
Q

Conduction

A

Heat transfer occurring through collisions of electrons and molecules in which they exchange energy.

57
Q

Hot fluid _____ while cold fluid ____

A

Rises

Sinks

58
Q

Convection

A

Like conduction, but at least one medium is a moving fluid.

59
Q

What would happen to the rate of convection if the fluid stopped moving?

A

It would decrease to zero because the temperature difference would decrease to zero at the interface

60
Q

What is the equation below for?

dQ/dt= AσεT^4

A

Radiation from one surface

61
Q

What is the equation below for?

dQ/dt~ h rad A dT

A

Radiation between two surfaces

62
Q

Radiation

A

The electromagnetic waves emitted and absorbed by all objects

63
Q

Emissivity

A

The measure of an object’s ability to emit infrared energy

From 0-1.0

64
Q

Blackbody

A

An object with an emissivity of 1.0

65
Q

Which have higher emissivity, dull black surfaces, or shiny metallic surfaces?

A

Dull black surfaces

66
Q

Which region is the radiation emitted by objects at body temperature in?

A

Infrared

67
Q

In the equation below, what do the symbols stand for?

dU= Q - W + E

A

dU is the change in internal energy

Q is the heat input (usually negative for humans)

W is the work done

E is the energy input (food)

68
Q

Metabolic energy input

A

E - dU

Energy input of food - change in internal energy

PHSI (6 decks)

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