Module 3: Thermodynamics

Question 1

Minimum value of Kelvins

Answer 1

0K

Question 2

How can temperature be changed?

Answer 2

By transfer of thermal energy

Question 3

How can a constant-volume gas thermometer be used?

Answer 3

By comparing with a triple point cell

T/Ttp = P/Ptp

Question 4

Secondary thermometers and how they are made accurate

Answer 4

One which is practical for general use

Calibrated against a primary thermometer

Question 5

Thermal energy

Answer 5

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

Question 6

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

Answer 6

Temperature (not thermal energy)

Question 7

Heat transfer

Answer 7

Movement of thermal energy

Higher nervy molecules share energy with lower energy molecules

Occurs until thermal equilibrium is reached

Question 8

Thermal equilibrium

Answer 8

When both objects are the same temperature

Question 9

Why does thermal expansion occur?

Answer 9

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

Question 10

α (thermodynamics)

Answer 10

Expansion coefficient

Question 11

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

Answer 11

2α and 3α

Question 12

Ideal gases all have the same ____?

Answer 12

Volume expansion coefficient

Question 13

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

Answer 13

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

Atoms/ molecules don’t stick together

Question 14

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

Answer 14

The more particles, the greater the increase in volume

Question 15

Which two laws contribute to the ideal gas law?

Answer 15

Charles’ law and Boyle’s law

Question 16

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

Answer 16

Total number of atoms/ molecules

Question 17

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

Answer 17

Boltzmann constant

1.38 x 10^-23 J K^-1

Question 18

n = N/?

Answer 18

NA (Avogadros constant)

Question 19

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

Answer 19

Both

Question 20

Dalton’s law

Answer 20

P = P1 + P2

Question 21

ppm

Answer 21

Parts per million

Question 22

Partial pressure

Answer 22

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

Question 23

Temperature is a measure of (apart from heat)?

Answer 23

Average kinetic energy per atom/ molecule

Question 24

________

1/2mv^2

Answer 24

Average kinetic energy per molecule

Question 25

U (thermodynamics)

Answer 25

Total kinetic energy

Question 26

What does the Maxwell-Boltzmann distribution show?

Answer 26

The molecules of a gas have a wide range of speeds

Question 27

What is the most common speed for O2 gas molecules?

Answer 27

400ms^-1

Question 28

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

Answer 28

When T is low enough | Or V is small enough

Question 29

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

Answer 29

Attractive forces between atoms of the gas cause them to stick together Gas condenses into a liquid or solid Called a phase change

Question 30

Does T change when phase changes?

Answer 30

No

Question 31

Saturated vapour pressure

Answer 31

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

Question 32

Does each substance have more than one vapour pressure?

Answer 32

Yes- at different temperatures

Question 33

How can we boil water at room temperature?

Answer 33

Decrease the pressure

Question 34

Why is thermal energy needed for phase change?

Answer 34

To overcome inter-atomic forces

Question 35

Q (thermodynamics)

Answer 35

Thermal energy input

Question 36

L (thermodynamics)

Answer 36

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

Question 37

kWh

Answer 37

Kilowatt hour | Equal to 3.6MJ

Question 38

First law of thermodynamics

Answer 38

Energy of an isolated system is constant

Question 39

Q = mcdT

Answer 39

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

Question 40

Specific heat capacity

Answer 40

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

Question 41

Dew-point temperature

Answer 41

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

Question 42

Is the partial pressure of water vapour usually more or less than the saturated vapour pressure? When are they equal?

Answer 42

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

Question 43

Moisture content in the air

Answer 43

The mass of moisture per kg of dry air

Question 44

Dry air

Answer 44

Air in our atmosphere containing nitrogen oxygen etc.

Question 45

Other names for moisture content (2)

Answer 45

Absolute humidity | Humidity ratio

Question 46

mw/ma

Answer 46

Humidity ratio Mass of water / mass of air

Question 47

Dry-bulb temperature

Answer 47

Normal air temperature

Question 48

Relative humidity

Answer 48

Partial water vapour pressure/ saturated vapour pressure at same T (Percentage humidity of what is possible)

Question 49

If given dew-point T and dry-bulb T How do you find the relative humidity in a psychometric chart?

Answer 49

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

Question 50

Wet-bulb temperature

Answer 50

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

Question 51

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

Answer 51

When RH= 100%

Question 52

Three forms of heat transfer

Answer 52

Conduction Convection Radiation

Question 53

dQ/dt

Answer 53

Rate of heat transfer

Question 54

h conduct

Answer 54

Conduction heat transfer coefficient h cond= k/d Where d = thickness

Question 55

What is k in thermodynamics?

Answer 55

Thermal conductivity

Question 56

Conduction

Answer 56

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

Question 57

Hot fluid _____ while cold fluid ____

Answer 57

Rises | Sinks

Question 58

Convection

Answer 58

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

Question 59

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

Answer 59

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

Question 60

What is the equation below for? dQ/dt= AσεT^4

Answer 60

Radiation from one surface

Question 61

What is the equation below for? dQ/dt~ h rad A dT

Answer 61

Radiation between two surfaces

Question 62

Radiation

Answer 62

The electromagnetic waves emitted and absorbed by all objects

Question 63

Emissivity

Answer 63

The measure of an object’s ability to emit infrared energy From 0-1.0

Question 64

Blackbody

Answer 64

An object with an emissivity of 1.0

Question 65

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

Answer 65

Dull black surfaces

Question 66

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

Answer 66

Infrared

Question 67

In the equation below, what do the symbols stand for? dU= Q - W + E

Answer 67

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)

Question 68

Metabolic energy input

Answer 68

E - dU Energy input of food - change in internal energy