Thermodynamic potentials Flashcards
What is the energy thermodynamic potential?
dE = Tds - pdV
Two applications: Mechanical equilibrium, isolated systems
What is the equation and an application of the Enthalpy thermodynamic potential?
Application: Flow processes (Joule-Kelvin expansion).
What is the equation and an application of Helmholtz free energy?
Application: Statistical Partition function, chemical reaction.
State Gibbs free energy and an application
Application: Phase equilibrium
Using this equation and the standard Free Helmholtz energy equation, find the internal energy of an ideal gas and the ideal gas law.
What is the difference between the Joule and Joule-Kelvin expansion?
Joule expansion is the free expansion of gas into a vacuum.
J-K expansion is a constrained expansion across a pressure drop where enthalphy is constant.
What is the Joule Coefficient?
Using reciprocity theorem, ideal gas equation and Joule coefficient, find the value of Joule’s coefficient for 1 mol of an ideal gas.
Using reciprocity equation, equation for Van der Waal gas and Joule expansion coefficient find the Joule coefficient for Van der Waal gases.
Does this gas cool or heat upon expansion?
Apply same process to get the alternate form of the Joule coeff. eq. Then plug in Van der Waal eq.
What is the alternate form of Joule’s coefficient?
Most RHS is alternate form found using reciprocity theorem.
State what is constant for flow processes.
Enthalpy is constant for flow processes,
dH = 0. H1 = H2.
Using the Joule-Kelvin coefficient, find the alternate form of the J-K coefficient.
State the alternate form of the J-K coefficient.
Note: The equation is the same for the Joule coefficient, but dp and dV have swapped positions.
For a phase change in equilibrium, what is the relation between the specific gibbs energy between two phases 1 and 2? Hint: dG = 0, considet a small mass dM transferred from phase 1 to 2.
State the Clausius-Clapeyron relation
Derive the Clausius-Clapeyron.
Hint 1: Consider the specific gibbs energy (div by mass). So can use relationship between specific gibbs entropy
Hint 2: Times by mass, to get entropy and Volume back from their specific counterparts.
Hint 3: Re-arrange for dP/dT and use latent heat equation ∆S = L/T
What is the relation for working out ∆T from the clapeyron relation once dP/dT has been found?
If you know Ti, use this to find Tf.
dp/dT = ∆p/∆T - rearrange
Tf = Ti + ∆T
STP 21, slides 12-14 for better visibility.
What is the third law of thermodynamics?
Using the equation on the RHS what happens to heat capacities as the temperatures approach 0 kelvin?
Using the third law, we know that the entropy becomes 0 as the temperature approaches 0. For the RHS to be 0, Heat capacity must vanish/ equal 0.
What happens to expansion coefficients as T approaches 0?
Image on this side with limits shows a better way of writing, but does not show where second expansion coefficient comes from.
Expansion coefficients approach 0 as T approaches 0, as dS = 0 for approaching 0.
Generalise the IE equation for a magnetic field.
Add a BdM term, then set for a fixed Volume, dV = 0. dE = Tds + BdM.
M is the Magnetisation. BdM is the magnitisation energy.
Using Curie’s Law provided (M term), and the Joule-Kelvin expansion coefficient, find whether adiabatic demagnetisation(akin to J-K expansion) would produce a cooling or heating effect.
