Thermodynamics Flashcards
What is the Zeroth Law of Thermodynamics?
If two objects are in thermal equilibrium with a third object, then they are in thermal equilibrium with each other.
What is the First Law of Thermodynamics?
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
What is the Second Law of Thermodynamics?
Any spontaneously occurring process will always lead to an increase in the entropy (S) of the universe.
(Second law, Spontaneous, increase in S)
What is the Third Law of Thermodynamics?
The entropy of a perfect crystal is zero when the temperature of the crystal is equal to absolute zero (0K).
What is an adiabatic wall?
An adiabatic wall is a wall that does not allow the transfer of heat from one side to the other.
What is a diathermal wall?
A diathermal wall is a wall that allows the transfer of heat from one side to the other.
In equilibrium, all intensive state variables are…?
In equilibrium, all intensive state variables are:
- Constant over time
- Uniform throughout the system
(e.g. pressure, temperature, density)
In what units is heat measured?
Joules
What is an intensive state variable?
Intensive: uniform throughout the system
What is an extensive state variable?
Extensive: adding up across the system
What does thermal equilibrium mean?
Having the same temperature.
What is heat flow?
Heat flow is a transfer of energy from one body to another due to a difference in temperature.
What is heat, Q?
Heat, Q (in J): A form of energy associated with temperature: the collective kinetic energy of all atoms in the system.
What is a reservoir?
Reservoir: A system large enough that a finite heat transfer won’t change its temperature.
Mechanisms of Heat Transfer
What is convection?
Convection is heat transfer by mass movement of molecules (in a liquid or gas).
Circulating convection currents
Mechanisms of Heat Transfer
What is radiation?
Radiation is made of electromagnetic waves which transport energy.
Does not require a medium like convection and conduction.
Mechanisms of Heat Transfer
What is conduction?
Conduction is the transfer of heat within a body or between two bodies in contact.
Molecular collisions transfer kinetic energy.
What is a state variable?
State variables: the physical quantities which describe the physical conditions in which a material exists.
Examples: Volume, pressure, temperature, mass
What is an equation of state?
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.
What are the conditions for thermodynamic equilibrium?
- All intensive state variables of a system are uniform throughout the system.
- All intensive state variables of a system are constant over time.
What is the difference between the thermodynamic concepts of steady state and equilibrium?
Intensive state variables are uniform across a system in equilibrium, but don’t need to be uniform for a steady state.
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?
As soon as all the ice has melted.
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…
…is done by the system.
Heat and work are _____ variables, but internal energy is a _____ variable and as such is _____ of how a system has reached its current state.
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.
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?
True.
What is the Kelvin-Planck statement of the 2nd Law?
There is no cycle that extracts heat from a reservoir and completely turns it into work.
What does isothermal mean?
Constant temperature.
What does isobaric mean?
Constant pressure.
What does isochoric mean?
Constant volume.
What is a system?
The thing we want to study.
What are the surroundings?
Everything else.
What is the universe?
System + Surroundings.
What is a quasi static process?
Slow enough that system can be treated as in equilibrium at all times.
It is a process that happens at an infinitesimally slow rate.
What is a spontaneous process?
A spontaneous process is one that occurs on its own, without any energy input from the outside.
What is expansion work?
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)
What is a cyclic process?
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.
What’s the equation for Helmholtz Free Energy?
F = U - TS
“Futs”
What’s the equation for enthalpy?
H = U + PV
“Hey, ur v pretty”
What’s the equation for the Gibb’s Function?
G = H - TS
“God, how terribly shit”
What is expansion work when the process is isobaric?
Constant pressure
W = p0ΔV
What is Carnot’s Theorem?
● All reversible engines have the same efficiency.
● No irreversible engine can be more efficient.
(provided they operate between the
same reservoirs)
What is the efficiency of an engine?
e = (W / Qh) x 100
Where:
W = |Qh| - |Qc|
What is the efficiency of a reversible process?
e = 1 - (Tc) / (Th)
What is the efficiency of an irreversible process?
e = 1 - (Qc) / (Qh)
What are heat and work in terms of kinetic energy?
Heat is disordered kinetic energy.
Work is ordered kinetic energy.
What is the equation for relaxation time?
Relaxation time, τ, is defined as:
x = x0 exp ( -t / τ )
Define the term relaxation in a thermodynamic context.
A process approaching equilibrium.
Define heat capacity.
The heat capacity of a substance is the amount of heat required to change its temperature by one degree.
Define latent heat.
Latent heat is the heat required to change a material’s state without change of temperature.
What is Gibb’s Phase Rule?
F = C - P + 2
F = degrees of freedom
C = number of components
P = number of phases
What is the triple point?
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.
What is the Clausius-Clapeyron equation?
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
Give examples of first order phase transitions.
Boiling, melting, sublimation
What is a first order phase transition?
First-order phase transitions are those that involve a latent heat.
Describe a first order phase transition.
● Latent heat > 0
● Abrupt change of G
● Step in S
● Singularity in Cp
What is a second order phase transition?
Also called “continuous phase transitions”, they do not involve latent heat.
Describe a second order phase transition.
● Latent heat = 0
● Gradual change of G
● Abrupt change of S
● Step in Cp
What is the first Ehrenfest equation?
dP / dT = ΔCp / T V Δα
Where:
● Cp is the heat capacity
● α is the thermal expansion
What is the second Ehrenfest equation?
dP / dT = Δα / Δκ
Where:
● α is the thermal expansion
● κ is the compressibility
Relationships between state
variables
What is the equation for dU?
dU = +TdS - pdV
Relationships between state
variables
What is the equation for dH?
dH = +TdS + VdP
Relationships between state
variables
What is the equation for dF?
dF = - SdT - pdV
Relationships between state
variables
What is the equation for dG?
dG = -SdT + VdP
Define the partition function.
Functions of the thermodynamic state variables.
E.g. the temperature and volume.
Give the equation for the partition function.
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
What is the equation for thermodynamic beta, β, in the context of statistical mechanics?
β = 1 / k(B) T
Where:
● k(B) is Boltzmann’s constant
● T is temperature
Define the term ‘macrostate’ in the context of statistical mechanics.
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.
Define the term ‘microstate’ in the context of statistical mechanics.
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.
Define the term ‘degeneracy’ , g(i).
Degeneracy is the number of states with the same energy.
Define the term relaxation in a thermodynamic context.
Relaxation describes the approach of a system to equilibrium after a disturbance.
It follows an exponential time dependence.
How many components and phases are there in ice cream?
● Two components: water and fat.
● Three phases in thermal equilibrium with each other: liquid water, solid water and solid fat.
For arbitrary N, how many microstates in the system are there?
Ωtot = 2^(N)
For arbitrary N, how many macrostates in the system are there?
N + 1
What is the equation for Boltzmann Entropy?
S = k(B) log Ω
What does the symbol Ω represent in the context of statistical mechanics?
Ω is the number of microstates.
What is Stirling’s Approximation?
log(N!) = N log (N) - N
What is the equation for Information Entropy? (Also known as “Shannon Entropy”)
I = -Σ(j) p(j) log p(j)
What is the Van-der-Waals equation?
(p + a / V(m)^2) (V(m) - b) = RT
What is an isotherm path?
An isotherm is a path at a constant temperature.
What is an adiabatic path?
An adiabatic is a path with no heat exchange.
What is a miscibility gap?
Region in the phase diagram where two phases of the same
state of matter coexist.
What is the efficiency of a heat engine?
Ratio of desired outputs to required inputs.
