Thermomdynamics Flashcards
What is another way of saying molar gibbs energy. Intensive/extensive?
Chemical potential μ, intensive
What is an extensive property
They are proportional to the amount of substance (at const T, P and composition) for example volume!
What is an intensive property
They are independent of of the amount of substance eg density, temp
The ratio of 2 extensive properties gives what
An intensive prop
How can you easily turn for example U, S and V into intensive properties
Devide by mols so its molar volume etc
What has no well-defined 0 value
Energy
What does isothermal mean
Constant temp but pressure variation
What happens to chemical potential when pressure increases
Chem pot increases too
For an ideal gas, does internal energy depend on pressure?
NO
What is Am
Molar Helmholtz energy
What does isobaric mean
Constant pressure, variation with T
Equation of molar internal energy of an ideal monatomic gas
Um = 3/2 RT + constant where constant is independent of P and T
What does adiabatic mean
Constant entropy and no heat change - thermally insulated system is compressed/expanded quickly
What happens during adiabatic heating
Rapid compression of a fluid raises its temp. Mechanicl E into heat E. Process that occurs without transferring heat or mass to environment.
Equation for temperature rise of ideal gas
dT = dU / Cv where dU is amount fo mechanical (compression) work done on gas
What is the enthalpy change of a mixture of ideal gases + why
0 bc they don’t interact
How is a pure liquid denoted to distinguish it from a component of a mixture
- for example μ*
What is assumed to be constant for ideal mixtures
Temp and Press
What is Raoult’s law in words
The vapour pressure of a solvent above solution = The mole fraction of solvent * Vapour pressure of pure solvent
When is G minimised in relation to a pure solvent + its vapour
If the chemical potential of liquid = vapour aka at equilibrium
When is the boiling point of a liquid
The temp when its vapour pressure is equal to the pressure of the gas above it eg 1bar in STP (P*A = P0)
In an ideal mixture, how is the vapour pressure compared to the pure vap press?
Pa < Pa, raoults law says vapour pressure is equal to mole fractionpure vapour pressure
Why is partial pressure in a mix less than pure vapour pressure in ideal? 2 reasons
- Fewer A molecs at surface = slower evaporation rate = slower condense rate at eq BUT equal condensation rate than pure A.
- Condensation rate only influenced by collisions of gas qith liquid surface = Since T and intermolecular forces = const then only lower vapour pressure can affect the rate
How does BP and freezing temp change if solute A is dissolved in solvent
BP increases and freezing point decreases