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MS3 > Thermodynamics I > Flashcards

Thermodynamics I Flashcards

1
Q

What is thermodynamics?

A

Thermodynamics summarises the properties of energy and its transformation from one form to another.

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2
Q

When studying the universe in thermodynamics, what two things can we split it into?

A

System and surroundings.

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3
Q

What is a system?

A

The subject that we are interested in.

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4
Q

What are surroundings?

A

The remainder of the universe outside the system.

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5
Q

What is an open system?

A

A system where energy and matter can be transferred with the surroundings.

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6
Q

What is a diathermic (closed) system?

A

A system where only energy can be transferred with the surroundings.

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7
Q

What is an adiabatic system?

A

A system where neither energy or matter can be transferred with the surroundings.

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8
Q

What are the two properties that the system depends on?

A

Extensive and intensive properties.

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9
Q

What are extensive properties?

A

They depend on the quantity of matter in the system, eg mass, volume.

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10
Q

What are intensive properties?

A

They are independent of the amount of matter present, eg temperature, density.

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11
Q

What is work?

A

Work is a motion against an opposing force.

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12
Q

When is work done?

A

Work is done when a force moves.

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13
Q

Do chemical changes do work?

A

Yes, they may release electrical or light energy as a result of doing work.

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14
Q

Most common form of work in Thermodynamics I?

A

pV work.

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15
Q

What happens for pV work to be done?

A

Work is done to increase the volume against the surrounding pressure.

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16
Q

What is energy in thermodynamics?

A

The capacity of a system to do work.

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17
Q

What is heat?

A

A means of transferring energy (process), it is not a form of energy!

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18
Q

What is internal energy?

A

The total KE due to motion of particles and PE associated with atoms within the molecules.

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19
Q

What scale is internal energy on?

A

The microscopic.

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20
Q

What is the symbol for internal energy?

A

U.

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21
Q

For a simple idea gas, all internal energy is what?

A

KE

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22
Q

What temperature is raised in an idea gas, what happens to U?

A

U increases as the KE of the particles increases.

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23
Q

What does +q show?

A

Heat going into the system (endo).

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24
Q

What does -q show?

A

Heat is given out by the system (exo).

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25
Q

What does +w show?

A

Work is done on the system (eg gas is compressed).

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26
Q

What does -w show?

A

Work is done by the system (eg gas expanding).

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27
Q

-w is also the same as…

A

…w’

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28
Q

(Ideal piston) what are the conditions for the gas to expand?

A

Pint>Pext

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29
Q

(Ideal piston) how much does the piston move?

A

dx

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30
Q

(Ideal piston) how much work is done for the expansion?

A

dw’

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31
Q

Due to dw’ = Fdx, F=PextA and Adx=dV, what is a formula for work done on a gas?

A

dw’=PextdV

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32
Q

(Ideal piston) if Pext=0 what can be said about the expansion of a gas?

A

There is no work done in expanding the gas.

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33
Q

(Ideal piston) if Pext=constant what can we do to find the work done?

A

Integrate dw’=PextdV.

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34
Q

First Law of Thermodynamics:

A

Energy can neither be created nor destroyed on transformed from one form to another.

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35
Q

First Law of Thermodynamics equation (U):

A

ΔU = Ub - Ua

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36
Q

Equation for ΔU with work and heat:

A

ΔU = q + w

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37
Q

q and w are what kind of functions?

A

Path functions.

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38
Q

What is a state function?

A

A function whose value depends only on the state of the material under consideration. It has the same value for a given state no matter how the state came about.

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39
Q

What is a path function?

A

A function whose value depends on the path which the system takes between two states.

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40
Q

Reversible change in U equation:

A

dU = dq + dw

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41
Q

Reversible change in U equation assuming only pV work:

A

dU = dq - PextdV

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42
Q

Can state and path functions be integrated?

A

Only state functions can be integrated as they are exact differentials.

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43
Q

What are the conditions for maximum work to be done?

A

External pressure should be as high as possible without exceeding the internal pressure.
Pext should be infinitesimally smaller than Pint.

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44
Q

Thermodynamic Equilibrium:

A

A system is in equilibrium with its surroundings if an infinitesimally small change in conditions in either direction will result in change of state in opposite directions.

45
Q

Reversible processes are linked to equilibrium how?

A

If a system is at equilibrium with its surroundings then an infinitesimal change can take place causing a change in state so the system is reversible.

46
Q

If a system is not in equilibrium can the process of expansion be thermodynamically reversible?

A

No it is irreversible.

47
Q

Features of reversible processes:

A

Infinitely slow.
At equilibrium.
Do maximum work.

48
Q

Features of irreversible processes:

A

Finite rate.
Not at equilibrium.
Do less than maximum work.

49
Q

At constant volume can pV work be done?

A

No, pV work cannot be done, all heat absorbed goes into internal energy.

50
Q

At constant volume, when we supply energy to an object, what is the relationship between the heat supplied and temperature rise?

A

dq = CdT

C is the heat capacity

51
Q

For a process at constant volume, how is the heat and internal energy related to temperature?

A

dU = dq(V) = C(V)dT

52
Q

What does the Equipartition of Energy state:

A

That the motion of an atom in any direction is equally likely and contributes an average of 1/2kt for each degree of freedom (Ideal Gas).

53
Q

At constant pressure, some heat will do what?

A

Some will increase the internal energy and some will appear as the work of expansion.

54
Q

For a fixed amount of heat, the change in internal energy is greater or less for a system at constant pressure compared to one at constant volume?

A

It is less as less energy remains in the system, the temperature rises less than a system with constant volume (heat capacity higher).

55
Q

Equation for enthalpy linking internal energy and work of expansion:

A

H = U + pV

56
Q

Small change in enthalpy equation:

A

dH = dU + pdV + Vdp

57
Q

If a process only has pV work, what does the small change in enthalpy equation become?

A

dH = dq + Vdp

as dU=dq-pdV so sub in

58
Q

Equation for enthalpy change at constant pressure:

A

dH = dq(p)

as at constant surrounding pressure, dp=0

59
Q

What can the enthalpy change be identified as?

A

The same as the energy supplied as heat.

60
Q

What can we measure about enthalpies?

A

We can only measure changes in enthalpies rather than enthalpies themselves.

61
Q

What assumption can we make about C(p)?

A

C(p) is constant.

62
Q

What is a more accurate form of C(p)?

A

C(p) = a + bT + c/(T^2)

where a, b and c are constants and depend on the substance.

63
Q

What is Hess’s Law:

A

Enthalpy change for a process is the same no matter what pathway we take in going from initial to final state.

64
Q

Explain Kirchhoff’s Equation:

A

See lecture notes, involves enthalpy changes of a reaction at a different temperature.

65
Q

What does the second law allow us to do?

A

Predict whether a reaction is spontaneous.

66
Q

Entropy is associated with what?

A

Disorder.

67
Q

Work simulates what?

A

A uniform (ordered) motion of atoms.

68
Q

Heat simulates what?

A

Disordered motion of atoms.

69
Q

The thermodynamic definition of entropy is motivated by what?

A

The idea that change in entropy depends on how much energy is transferred as heat.

70
Q

Definition of entropy equation:

A

dS = q(rev)/T

71
Q

When is a process spontaneous?

A

When the entropy of the universe increases.

72
Q

What do we do if a process is not reversible and we want to calculate the entropy change of the system?

A

We calculate the heat change to the system if the process took place reversibly.

73
Q

In an isothermal process, what happens to dU?

A

dU=0

74
Q

What is the enthalpy change of the surroundings due to heat exchange with the system?

A

H(surr,final) – H(surr,initial) = dH(surr) = q(rev,surr)

75
Q

Why does a change in state only depend on the amount of heat, independent as to whether it was supplied reversibly?

A

Enthalpy is a state function.

dH(surr) = q(rev,surr) = q(surr) = –q(sys)

76
Q

How can we use q(surr) = –q(sys) to find the entropy change of the universe in terms of the system?

A

dS(surr) = –q(sys)/T(surr)

dS(univ) = dS(sys) – q(sys)/T(surr)

77
Q

Derive an expression involving Cp for the variation of entropy with temperature.

A

Check derivation.

78
Q

How does entropy change at phase changes?

A

It changes by a certain value related to the ∆H of transformation.

79
Q

State the Gibbs function and the Helmholtz function.

A 
G = H - TS
A = U - TS
80
Q

What conditions is the Gibbs function valid for?

A

Constant pressure.

81
Q

What conditions is the Helmholtz function valid for?

A

Constant volume.

82
Q

Derive an expression relating G and the entropy of the universe.

A

Check derivation

83
Q

Relate maximum work under reversible conditions and G.

A

Check derivation

84
Q

Derive and stater the 3 master equations.

A

Check

85
Q

Derive the molar Gibbs energy relation.

A

Check derivation

86
Q

Derive the Gibbs-Helmholtz equation.

A

Check derivation

87
Q

Derive an expression for the free energy of mixing of ideal gases.

A

Check derivation

88
Q

Derive an expression relating G to K using chemical potentials.

A

Check derivation

89
Q

Derive Van’t Hoff Isochore law.

A

Check derivation

90
Q

Integrate the Van’t Hoff Isochore law.

A

Check

91
Q

Using a statistical definition of entropy, derive the entropy of mixing and compare to the result from the Gibbs equation.

A

Check derivation

92
Q

What is an Ellingham plot of?

A

Standard free energy, when 1 mole of gaseous O2 reacts with a pure element to form an oxide as a function of temperature, T.

93
Q

3 main uses of an Ellingham diagram.

A

Determine the relative ease of reducing a metallic oxide.
Determine the partial pressure of O2 in equilibrium with a metal oxide at a given temperature.
Determine the ratio of carbon monoxide to carbon dioxide that will reduce a metal oxide at a given temperature.

94
Q

What does position on an Ellingham diagram show?

A

The affinity of a metal for oxygen, lower means highly reactive and more difficult to reduce.

95
Q

On an Ellingham diagram, a carbon reaction can reduce any metal oxide, when?

A

When it is below the metal oxide reaction.

96
Q

Why is it more difficult to extract metals from sulfides using hydrogen or carbon?

A

They have a lower affinity for sulfur than they do for oxygen.

97
Q

List the reactions with oxygen for removing a metal from its sulfide.

A

Check list

98
Q

What equation is a Kellogg diagram built on?

A

∆G˚ = -RTlnK

99
Q

Derive the phases rule.

A

Check derivation

100
Q

Derive the Clapeyron equation

A

Check derivation

101
Q

Consider the Clapeyron equation at solid->gas and liquid->gas transitions.

A

Check

102
Q

Consider the Clapeyron equation for solid->liquid transitions.

A

Check

103
Q

Derive the Clausius-Clapeyron equation.

A

Check derivation

104
Q

Give expressions for Raoult’s law

A

Check

105
Q

When is Raoult’s law valid?

A

For ideal solutions..

106
Q

When is Henry’s Law valid?

A

For non-ideal solutions when solute is very diluted.

107
Q

Give an expression for Henry’s law.

A

Check

108
Q

Derive an expression for the free energy of mixing of a regular solution.

A

Check derivation.

109
Q

What is the enthalpy change of mixing of an ideal solution.

A

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