Thermodynamics_Flashcards_Combined
(168 cards)
1
Q
What is a thermodynamic system?
A
A defined region of space (e.g., a gas in a container) separated by boundaries from the surroundings.
2
Q
What are the surroundings in thermodynamics?
A
Everything outside the system that can interact with it.
3
Q
What is meant by ‘macroscopic’ in thermodynamics?
A
A large-scale view of a system described by measurable properties like pressure, volume, and temperature.
4
Q
What is ‘microscopic’ in thermodynamics?
A
Describes systems in terms of particles and their interactions, such as position and momentum of atoms.
5
Q
What are examples of macroscopic properties?
A
Temperature, pressure, volume, internal energy.
6
Q
What does conservation of energy imply in thermodynamics?
A
The total energy (kinetic + potential + internal) in an isolated system remains constant.
7
Q
What kind of energy does a spring-mass system possess?
A
Kinetic and potential energy.
8
Q
What happens when damping is removed from a spring-mass system?
A
The system oscillates without energy loss.
9
Q
What is internal energy?
A
The total energy contained within a system, including kinetic and potential energy at the microscopic level.
10
Q
Why do we use average properties in thermodynamics?
A
Because systems contain a huge number of particles, averages simplify analysis.
11
Q
What is the role of temperature in thermodynamics?
A
It quantifies the average kinetic energy of particles in a system.
12
Q
What makes a thermodynamic description useful?
A
It relates macroscopic parameters to energy transformations and system behavior.
13
Q
What is a closed system in thermodynamics?
A
A system that can exchange energy (heat or work) but not matter with its surroundings.
14
Q
What is an isolated system?
A
A system that does not exchange energy or matter with its surroundings.
15
Q
What is an open system?
A
A system that can exchange both energy and matter with its surroundings.
16
Q
How is work defined in thermodynamics?
A
Work done by the system is considered positive.
17
Q
What defines a thermodynamic state?
A
A unique set of macroscopic parameters such as pressure, volume, and temperature.
18
Q
What is a process in thermodynamics?
A
A transition between two equilibrium states of a system.
19
Q
What is meant by ‘relaxation time’?
A
The time a system takes to return to equilibrium after a disturbance.
20
Q
What does local equilibrium mean?
A
Even if the entire system is not in equilibrium, small regions within it can be treated as if they are.
21
Q
What are intensive properties?
A
Properties that do not depend on system size (e.g., temperature, pressure).
22
Q
What are extensive properties?
A
Properties that depend on system size or mass (e.g., volume, energy).
23
Q
What does the thermodynamic postulate state?
A
Only a small number of extensive parameters are needed to define the thermodynamic state.
24
Q
Why are intensive variables useful?
A
They can vary from point to point in space, helping define local equilibrium.
25
What is the First Law of Thermodynamics?
ΔU = Q − W, where ΔU is the change in internal energy, Q is heat added, and W is work done by the system.
26
Is ΔU path dependent?
No, ΔU depends only on the initial and final states, not the path taken.
27
Are heat (Q) and work (W) path dependent?
Yes, both Q and W depend on the process path.
28
What does it mean if ΔU = 0?
The process is cyclic, or the internal energy returns to its initial value.
29
What is a reversible process?
An idealized process that occurs infinitely slowly, allowing the system to remain in equilibrium.
30
How does work compare in adiabatic vs isothermal expansion?
Adiabatic expansion does more work than isothermal for the same pressure change.
31
In a cyclic process, what does the net work equal?
The area enclosed in a PV diagram.
32
What is true for a heat engine operating in a cycle?
It absorbs heat Q_in and produces work W_net, rejecting heat Q_out.
33
How is work represented in a PV diagram?
As the area under the process curve.
34
How is a process path defined thermodynamically?
By specifying how pressure, volume, and temperature change between states.
35
What is a quasistatic process?
A process that proceeds infinitely slowly, keeping the system in near-equilibrium.
36
Why is PdV not defined for non-quasistatic processes?
Because pressure may not be uniform throughout the system.
37
What is a reversible process in thermodynamics?
An ideal process that can be reversed without leaving any net change in system or surroundings.
38
What is the Carnot cycle?
A theoretical cycle that represents the most efficient heat engine operating between two temperatures.
39
What are the four steps of the Carnot cycle?
Isothermal expansion, adiabatic expansion, isothermal compression, adiabatic compression.
40
What does a PV diagram of a Carnot cycle look like?
Two isothermal and two adiabatic curves forming a closed loop.
41
Why is the Carnot cycle important?
It sets the upper limit on the efficiency of any heat engine.
42
What is the condition for maximum efficiency in heat engines?
The engine must operate in a completely reversible cycle.
43
How does the Carnot efficiency formula relate to temperature?
η = 1 − T_cold / T_hot, where temperatures are in Kelvin.
44
What does a closed loop in a PV diagram represent?
A cyclic process, with net work equal to the area enclosed by the loop.
45
What is the Second Law of Thermodynamics (Kelvin–Planck statement)?
No process is possible whose sole result is the absorption of heat from a reservoir and its complete conversion into work.
46
What is the Clausius statement of the Second Law?
Heat cannot spontaneously flow from a colder body to a hotter one.
47
What is the working principle of a heat engine?
It absorbs heat from a hot reservoir, performs work, and releases heat to a cold reservoir.
48
What is the efficiency (η) of a heat engine?
η = W_out / Q_in = 1 − Q_out / Q_in
49
What is a refrigerator in thermodynamics?
A device that moves heat from a cold space to a hot one by doing work.
50
What is a heat pump?
A system that transfers heat into a hot region using external work.
51
What does a Carnot engine demonstrate?
That the maximum efficiency of a heat engine depends only on reservoir temperatures.
52
How is Carnot efficiency calculated?
η_Carnot = 1 − T_cold / T_hot (in Kelvin)
53
Can Carnot efficiency be achieved in practice?
Only for ideal reversible processes; real engines are less efficient.
54
What is true for cyclic processes over one complete cycle?
The net change in internal energy (ΔU) is zero.
55
Why are the Kelvin–Planck and Clausius statements equivalent?
Because violating one implies the violation of the other, as both describe impossible conversions of heat and work.
56
What happens if a heat engine violates the Clausius statement?
It would enable heat to flow from cold to hot without work, allowing perpetual motion.
57
What does the Second Law say about net work in a full cycle?
The total change in internal energy is zero; net work equals net heat exchanged.
58
Can any engine be more efficient than a Carnot engine?
No — the Carnot engine sets the maximum theoretical efficiency between two temperatures.
59
What does comparing an arbitrary engine to a Carnot engine show?
Any engine less efficient than Carnot must release more heat to the cold reservoir.
60
How can Carnot principles apply to refrigerators?
They help define the minimum work required to extract heat from a cold body.
61
What does the Second Law restrict in practical systems?
It limits the direction of heat flow and maximum efficiency of energy conversion devices.
62
Can any engine be more efficient than a Carnot engine operating between the same two temperatures?
No, the Carnot engine has the maximum theoretical efficiency.
63
What happens if an engine is more efficient than a Carnot engine?
It would violate the Second Law of Thermodynamics.
64
What is required for truly reversible heat transfer?
The temperature difference between the system and reservoir must be infinitesimally small.
65
What is a thermal reservoir?
An idealized body with a large heat capacity that remains at constant temperature.
66
How does a Carnot engine interact with thermal reservoirs?
It absorbs and rejects heat reversibly at the temperatures of the reservoirs.
67
What happens in any cyclic engine interacting with two thermal reservoirs?
It must have efficiency less than or equal to that of a Carnot engine.
68
Why is reversibility important in thermodynamic comparisons?
Only reversible engines define ideal limits that real engines cannot surpass.
69
What is the Clausius inequality?
For any cyclic process: ∮(δQ / T) ≤ 0, with equality holding for reversible processes.
70
What does the Clausius inequality imply for irreversible cycles?
That the total entropy change is negative, indicating irreversibility.
71
What is the definition of entropy (S)?
dS = δQ_rev / T for a reversible process.
72
Why is entropy considered a state function?
Because the entropy change between two states is independent of the path taken.
73
What is the total entropy change in a reversible cyclic process?
Zero: ∮(dS) = 0
74
What happens to entropy in an irreversible process?
The total entropy increases: ΔS > ∫(δQ / T)
75
Can entropy be used to define the direction of natural processes?
Yes, processes occur in the direction of increasing entropy.
76
How can entropy change between two states be calculated?
By integrating dS = δQ_rev / T over any reversible path connecting the states.
77
What is the physical meaning of entropy?
A measure of the disorder or number of microstates available to a system.
78
What is the condition for thermal equilibrium in terms of entropy?
Entropy is maximized at equilibrium for an isolated system.
79
What does the Second Law say about entropy in isolated systems?
The total entropy of an isolated system can never decrease: ΔS_universe ≥ 0.
80
What is the entropy change when two bodies come into thermal contact?
The total entropy change is the sum of the entropy changes of both bodies.
81
How is the entropy change of a body with constant heat capacity C calculated?
ΔS = C ln(T_final / T_initial).
82
If two identical blocks at different temperatures are brought into contact, what happens?
Heat flows from hot to cold, increasing total entropy.
83
What is the entropy change of the universe for two blocks reaching thermal equilibrium?
ΔS_universe = C ln(T_f/T_1) + C ln(T_f/T_2) > 0.
84
Can a block's entropy decrease in an irreversible process?
Yes, but the increase in the surroundings must outweigh the decrease.
85
What condition ensures that entropy change of the universe is positive?
T_final must lie between T_1 and T_2 such that both terms in ΔS_universe are positive.
86
What does ΔS_universe = 0 imply about the process?
That the process is reversible.
87
Why do we model blocks with constant heat capacity?
To simplify entropy calculations during temperature change.
88
How does the Second Law guide directionality of spontaneous processes?
They proceed in the direction that increases total entropy.
89
What is the entropy change for a reversible process?
ΔS = ∫(δQ_rev / T), calculated over a reversible path.
90
How is the entropy change of an ideal gas derived?
Using δQ_rev and applying the First Law to an ideal gas transformation.
91
What is the entropy change of an ideal gas between two states (T1, V1) and (T2, V2)?
ΔS = nC_V ln(T2/T1) + nR ln(V2/V1)
92
What is the entropy change during an isothermal expansion of an ideal gas?
ΔS = nR ln(V2/V1), since T is constant.
93
What is the entropy change of surroundings if heat transfer is reversible?
ΔS_surroundings = −Q/T, for constant T heat reservoir.
94
What happens to entropy in an adiabatic reversible process?
ΔS = 0, since no heat is exchanged (Q = 0).
95
What is the sign of entropy change for irreversible expansion?
Positive — total entropy increases.
96
Why does entropy not change in an adiabatic reversible process?
Because there is no heat flow: δQ = 0 ⇒ ΔS = 0.
97
How can we evaluate entropy change for complex paths?
Use a reversible path between the same initial and final states.
98
In what unit is entropy typically expressed?
Joules per Kelvin (J/K).
99
What is the fundamental thermodynamic relation?
dU = TdS − PdV
100
What are the natural variables of internal energy?
Entropy (S) and volume (V): U = U(S, V)
101
How is the First Law expressed differentially?
dU = δQ + δW = TdS − PdV for reversible processes.
102
What is the interpretation of dU = TdS − PdV?
A reversible change in internal energy is due to heat added and work done on the system.
103
How is δW defined for a quasistatic expansion?
δW = −P dV
104
What makes U a state function?
It depends only on the current state (S, V), not the path taken.
105
Can U be expressed as a function of other variables?
Yes, via Legendre transforms to H(S, P), A(T, V), or G(T, P).
106
Why is TdS − PdV useful in thermodynamics?
It allows derivation of other thermodynamic potentials and Maxwell relations.
107
What is implied by dU being an exact differential?
That internal energy is a state function and path-independent.
108
What is an example of an intensive and extensive variable pair?
T (intensive) with S (extensive); P (intensive) with V (extensive).
109
What is the enthalpy H(S, P) defined as?
H = U + PV
110
What is the differential form of enthalpy?
dH = TdS + VdP
111
What is the Helmholtz free energy F(T, V)?
F = U − TS
112
What is the differential form of Helmholtz free energy?
dF = −S dT − P dV
113
What is the Gibbs free energy G(T, P)?
G = U + PV − TS
114
What is the differential form of Gibbs free energy?
dG = −S dT + V dP
115
What does each thermodynamic potential represent?
A new state function adapted to different constraints (T, P, V, S).
116
What does a Legendre transform do in thermodynamics?
It changes the natural variables of a function by subtracting a conjugate variable term.
117
Which potential is useful at constant temperature and volume?
Helmholtz free energy, F(T, V)
118
Which potential is useful at constant temperature and pressure?
Gibbs free energy, G(T, P)
119
What condition defines equilibrium in an isolated system?
Entropy is maximized: δS = 0, and system is in stable equilibrium.
120
What is minimized at constant S and V?
Internal energy U is minimized.
121
What is minimized at constant T and V?
Helmholtz free energy F is minimized.
122
What is minimized at constant T and P?
Gibbs free energy G is minimized.
123
What is the physical significance of minimizing G?
Spontaneous processes at constant T and P reduce G until equilibrium.
124
How are equilibrium criteria related to thermodynamic potentials?
Each potential gives the direction of spontaneous change under different constraints.
125
What is the total differential of internal energy?
dU = TdS − PdV
126
What kind of mathematical operation yields Maxwell relations?
Taking second derivatives of thermodynamic potentials and applying equality of mixed partials.
127
What does the equality of mixed partials imply in thermodynamics?
Each thermodynamic potential gives rise to a Maxwell relation.
128
Why are Maxwell relations useful?
They relate measurable properties like temperature, pressure, and volume to entropy and energy.
129
What are Maxwell relations derived from?
The equality of mixed partial derivatives applied to thermodynamic potentials.
130
What is the Maxwell relation from U(S, V)?
(∂T/∂V)_S = −(∂P/∂S)_V
131
What is the Maxwell relation from H(S, P)?
(∂T/∂P)_S = (∂V/∂S)_P
132
What is the Maxwell relation from F(T, V)?
(∂S/∂V)_T = (∂P/∂T)_V
133
What is the Maxwell relation from G(T, P)?
(∂S/∂P)_T = −(∂V/∂T)_P
134
What are phases in thermodynamics?
Distinct forms of matter such as solid, liquid, and gas.
135
What is a phase transition?
A change of a substance from one phase to another, e.g., melting, vaporization.
136
What does a phase diagram show?
The conditions (P, T) under which distinct phases exist and coexist.
137
What is meant by degrees of freedom in a phase diagram?
The number of independent intensive variables that can be changed without altering the number of phases.
138
Why do constraints increase during phase coexistence?
Because intensive variables become linked by equilibrium conditions between phases.
139
What conditions define phase equilibrium?
Equal temperature, pressure, and chemical potential between phases: T₁ = T₂, P₁ = P₂, μ₁ = μ₂
140
What is the Clausius-Clapeyron equation?
dP/dT = ΔS / ΔV = L / (T ΔV), where L is latent heat.
141
What does the slope of a coexistence line in a P-T diagram represent?
The ratio of latent heat to temperature and volume change: dP/dT = L / (T ΔV)
142
Why is the Clausius-Clapeyron relation important?
It describes how pressure and temperature relate during phase transitions.
143
What is a phase boundary?
A line on a phase diagram where two phases coexist in equilibrium.
144
What are typical phase regions in a P-T diagram?
Solid, liquid, and gas, separated by coexistence lines and meeting at a triple point.
145
What is meant by local thermodynamic equilibrium?
The assumption that each small region of a non-uniform system behaves as if it is in equilibrium.
146
Why is local equilibrium useful?
It allows thermodynamic variables like entropy and pressure to be defined at each point.
147
What is a triple point?
A unique condition where three phases coexist in equilibrium.
148
Why must chemical potential be equal across phases?
To prevent net mass transfer and ensure equilibrium.
149
What is the relationship between latent heat and entropy change?
L = T ΔS, where L is latent heat and ΔS is the entropy change between phases.
150
What is the condition for phase coexistence in terms of Gibbs free energy?
G₁ = G₂ at equilibrium between two phases.
151
What is the differential form of chemical potential?
dμ = −S_m dT + V_m dP
152
How is the Clapeyron equation expressed using Gibbs free energy?
dP/dT = ΔS / ΔV = L / (T ΔV)
153
What happens to Gibbs free energy during a phase transition?
It remains continuous and equal for coexisting phases.
154
What is true about the slope of a phase boundary in a P-T diagram?
It equals the ratio of latent heat to the temperature times volume change: dP/dT = L / (T ΔV)
155
Why is specific Gibbs free energy used in phase calculations?
It allows tracking of individual phase contributions in multi-component or multi-phase systems.
156
How do you evaluate phase transitions at constant temperature?
Set dT = 0 in the Gibbs differential: dμ = V_m dP
157
How do you evaluate phase transitions at constant pressure?
Set dP = 0 in the Gibbs differential: dμ = −S_m dT
158
What ensures equilibrium in a two-phase system?
Equality of temperature, pressure, and chemical potential.
159
What is the Gibbs phase rule?
F = C − P + 2, where F = degrees of freedom, C = number of components, P = number of coexisting phases.
160
What does the Gibbs phase rule tell us?
How many independent variables can be changed without altering the number of phases.
161
What is the value of F at a triple point in a unary system?
F = 1 − 3 + 2 = 0, meaning no degrees of freedom — fixed P and T.
162
What is a triple point?
The unique condition at which three phases of a substance coexist in equilibrium.
163
What is a critical point?
The end point of a phase boundary beyond which liquid and gas are indistinguishable.
164
What does 'local equilibrium' mean in a non-uniform system?
Each small region behaves as if in thermodynamic equilibrium, enabling use of intensive variables locally.
165
Why is local equilibrium assumed in continuum thermodynamics?
It allows thermodynamic properties like temperature and pressure to be defined at a point.
166
What are the state postulates in thermodynamics?
The number of independent intensive properties needed to define the state of a system.
167
How many properties are needed to define the state of a simple compressible system?
Two independent intensive properties.
168
What does irreversible entropy production imply about real processes?
All spontaneous processes produce entropy, leading to ΔS_total > 0.
