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Engineering Physics Year 2 > Thermodynamics > Flashcards

Thermodynamics Flashcards

1
Q

What is the Zeroth Law of Thermodynamics?

A

If two objects are in thermal equilibrium with a third object, then they are in thermal equilibrium with each other.

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2
Q

What is the First Law of Thermodynamics?

A

Energy is conserved. It can be neither created nor destroyed.

ΔU = Q - W
(ur quite weird)

Change in internal energy = Heat added - Work done by system

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3
Q

What is the Second Law of Thermodynamics?

A

Any spontaneously occurring process will always lead to an increase in the entropy (S) of the universe.

(Second law, Spontaneous, increase in S)

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4
Q

What is the Third Law of Thermodynamics?

A

The entropy of a perfect crystal is zero when the temperature of the crystal is equal to absolute zero (0K).

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5
Q

What is an adiabatic wall?

A

An adiabatic wall is a wall that does not allow the transfer of heat from one side to the other.

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5
Q

What is a diathermal wall?

A

A diathermal wall is a wall that allows the transfer of heat from one side to the other.

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6
Q

In equilibrium, all intensive state variables are…?

A

In equilibrium, all intensive state variables are:

  • Constant over time
  • Uniform throughout the system

(e.g. pressure, temperature, density)

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7
Q

In what units is heat measured?

A

Joules

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8
Q

What is an intensive state variable?

A

Intensive: uniform throughout the system

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9
Q

What is an extensive state variable?

A

Extensive: adding up across the system

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10
Q

What does thermal equilibrium mean?

A

Having the same temperature.

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11
Q

What is heat flow?

A

Heat flow is a transfer of energy from one body to another due to a difference in temperature.

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12
Q

What is heat, Q?

A

Heat, Q (in J): A form of energy associated with temperature: the collective kinetic energy of all atoms in the system.

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13
Q

What is a reservoir?

A

Reservoir: A system large enough that a finite heat transfer won’t change its temperature.

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14
Q

Mechanisms of Heat Transfer

What is convection?

A

Convection is heat transfer by mass movement of molecules (in a liquid or gas).

Circulating convection currents

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15
Q

Mechanisms of Heat Transfer

What is radiation?

A

Radiation is made of electromagnetic waves which transport energy.

Does not require a medium like convection and conduction.

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16
Q

Mechanisms of Heat Transfer

What is conduction?

A

Conduction is the transfer of heat within a body or between two bodies in contact.

Molecular collisions transfer kinetic energy.

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17
Q

What is a state variable?

A

State variables: the physical quantities which describe the physical conditions in which a material exists.

Examples: Volume, pressure, temperature, mass

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18
Q

What is an equation of state?

A

Equation of state: the relationship between the state variables. It can be a graph, a numerical table or an actual equation.

An equation of state is a thermodynamic equation describing the state of matter under a given set of physical conditions.

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19
Q

What are the conditions for thermodynamic equilibrium?

A
  1. All intensive state variables of a system are uniform throughout the system.
  2. All intensive state variables of a system are constant over time.
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20
Q

What is the difference between the thermodynamic concepts of steady state and equilibrium?

A

Intensive state variables are uniform across a system in equilibrium, but don’t need to be uniform for a steady state.

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21
Q

A pot with water containing ice cubes is placed on a working cooking hob. When will the temperature measured in the water begin to rise?

A

As soon as all the ice has melted.

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22
Q

If a system undergoes an isothermal expansion, an isobaric contraction and an isochoric compression back to the starting point (in this order), the work during this cycle…

A

…is done by the system.

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23
Q

Heat and work are _____ variables, but internal energy is a _____ variable and as such is _____ of how a system has reached its current state.

A

Heat and work are (process) variables, but internal energy is a (state) variable and as such is (independent of) how a system has reached its current state.

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24
Q

When studying the thermodynamics of a water kettle, it is easier to calculate the system’s energy in terms of its enthalpy than its internal energy. True or False?

A

True.

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25
Q

What is the Kelvin-Planck statement of the 2nd Law?

A

There is no cycle that extracts heat from a reservoir and completely turns it into work.

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26
Q

What does isothermal mean?

A

Constant temperature.

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27
Q

What does isobaric mean?

A

Constant pressure.

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28
Q

What does isochoric mean?

A

Constant volume.

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29
Q

What is a system?

A

The thing we want to study.

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30
Q

What are the surroundings?

A

Everything else.

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31
Q

What is the universe?

A

System + Surroundings.

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32
Q

What is a quasi static process?

A

Slow enough that system can be treated as in equilibrium at all times.

It is a process that happens at an infinitesimally slow rate.

33
Q

What is a spontaneous process?

A

A spontaneous process is one that occurs on its own, without any energy input from the outside.

34
Q

What is expansion work?

A

W = ∫ pdV

Where the upper limit is Vf and the lower limit is Vi

Area under a P(V) curve

Sign convention:
W > 0: done BY the system
W < 0: done ON the system

W = nRT ln (Vf/Vi)

35
Q

What is a cyclic process?

A

A process in which the initial and final states are the same.

A series of changes which return the system back to its initial state.

36
Q

What’s the equation for Helmholtz Free Energy?

A

F = U - TS

“Futs”

37
Q

What’s the equation for enthalpy?

A

H = U + PV

“Hey, ur v pretty”

38
Q

What’s the equation for the Gibb’s Function?

A

G = H - TS

“God, how terribly shit”

39
Q

What is expansion work when the process is isobaric?

A

Constant pressure

W = p0ΔV

40
Q

What is Carnot’s Theorem?

A

● All reversible engines have the same efficiency.
● No irreversible engine can be more efficient.

(provided they operate between the
same reservoirs)

41
Q

What is the efficiency of an engine?

A

e = (W / Qh) x 100

Where:

W = |Qh| - |Qc|

42
Q

What is the efficiency of a reversible process?

A

e = 1 - (Tc) / (Th)

43
Q

What is the efficiency of an irreversible process?

A

e = 1 - (Qc) / (Qh)

44
Q

What are heat and work in terms of kinetic energy?

A

Heat is disordered kinetic energy.

Work is ordered kinetic energy.

45
Q

What is the equation for relaxation time?

A

Relaxation time, τ, is defined as:

x = x0 exp ( -t / τ )

46
Q

Define the term relaxation in a thermodynamic context.

A

A process approaching equilibrium.

47
Q

Define heat capacity.

A

The heat capacity of a substance is the amount of heat required to change its temperature by one degree.

48
Q

Define latent heat.

A

Latent heat is the heat required to change a material’s state without change of temperature.

49
Q

What is Gibb’s Phase Rule?

A

F = C - P + 2

F = degrees of freedom
C = number of components
P = number of phases

50
Q

What is the triple point?

A

The triple point is a point at which all three phases, solid, liquid and gas, can all coexist in equilibrium, due to a specific temperature and pressure.

51
Q

What is the Clausius-Clapeyron equation?

A

dP / dT = L / TΔV

Where:
● dP / dT is the slope of the tangent to the coexistence curve at any point
● L is the specific latent heat
● T is the temperature
● ΔV is the specific volume change of the phase transition

52
Q

Give examples of first order phase transitions.

A

Boiling, melting, sublimation

53
Q

What is a first order phase transition?

A

First-order phase transitions are those that involve a latent heat.

54
Q

Describe a first order phase transition.

A

● Latent heat > 0
● Abrupt change of G
● Step in S
● Singularity in Cp

55
Q

What is a second order phase transition?

A

Also called “continuous phase transitions”, they do not involve latent heat.

56
Q

Describe a second order phase transition.

A

● Latent heat = 0
● Gradual change of G
● Abrupt change of S
● Step in Cp

57
Q

What is the first Ehrenfest equation?

A

dP / dT = ΔCp / T V Δα

Where:
● Cp is the heat capacity
● α is the thermal expansion

58
Q

What is the second Ehrenfest equation?

A

dP / dT = Δα / Δκ

Where:
● α is the thermal expansion
● κ is the compressibility

59
Q

Relationships between state
variables

What is the equation for dU?

A

dU = +TdS - pdV

60
Q

Relationships between state
variables

What is the equation for dH?

A

dH = +TdS + VdP

61
Q

Relationships between state
variables

What is the equation for dF?

A

dF = - SdT - pdV

62
Q

Relationships between state
variables

What is the equation for dG?

A

dG = -SdT + VdP

63
Q

Define the partition function.

A

Functions of the thermodynamic state variables.

E.g. the temperature and volume.

64
Q

Give the equation for the partition function.

A

Z(1) = Σ(j) e ^(-β ε(j) )

Where:
● j is the microstates of the system
● e is euler’s number
● β is the thermodynamic beta
● ε(j) is the total energy of the system

65
Q

What is the equation for thermodynamic beta, β, in the context of statistical mechanics?

A

β = 1 / k(B) T

Where:
● k(B) is Boltzmann’s constant
● T is temperature

66
Q

Define the term ‘macrostate’ in the context of statistical mechanics.

A

A macrostate is a state of the system as a whole

which is realised by a number of different microstates

and whose thermodynamic variables are mean values of the contributing group of microstates.

67
Q

Define the term ‘microstate’ in the context of statistical mechanics.

A

A microstate is a specific configuration of a system

where each constituent particle is described by

its own position, energy, momentum and other extensive state variables.

68
Q

Define the term ‘degeneracy’ , g(i).

A

Degeneracy is the number of states with the same energy.

69
Q

Define the term relaxation in a thermodynamic context.

A

Relaxation describes the approach of a system to equilibrium after a disturbance.

It follows an exponential time dependence.

70
Q

How many components and phases are there in ice cream?

A

● Two components: water and fat.

● Three phases in thermal equilibrium with each other: liquid water, solid water and solid fat.

71
Q

For arbitrary N, how many microstates in the system are there?

A

Ωtot = 2^(N)

72
Q

For arbitrary N, how many macrostates in the system are there?

A

N + 1

73
Q

What is the equation for Boltzmann Entropy?

A

S = k(B) log Ω

74
Q

What does the symbol Ω represent in the context of statistical mechanics?

A

Ω is the number of microstates.

75
Q

What is Stirling’s Approximation?

A

log(N!) = N log (N) - N

76
Q

What is the equation for Information Entropy? (Also known as “Shannon Entropy”)

A

I = -Σ(j) p(j) log p(j)

77
Q

What is the Van-der-Waals equation?

A

(p + a / V(m)^2) (V(m) - b) = RT

78
Q

What is an isotherm path?

A

An isotherm is a path at a constant temperature.

79
Q

What is an adiabatic path?

A

An adiabatic is a path with no heat exchange.

80
Q

What is a miscibility gap?

A

Region in the phase diagram where two phases of the same
state of matter coexist.

81
Q

What is the efficiency of a heat engine?

A

Ratio of desired outputs to required inputs.

Engineering Physics Year 2 (6 decks)

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