Phase Equilibria Of Pure Substances Flashcards
What is relation between entropy of solid,liquid and gas
Sm(solid)<Sm(liquid)<Sm(gas)
What is critical temperature Tc
Above it liquid and gas are no longer estinguishablr andba single fluid exists called superficial fluid
What is phase boundary line
Line at certain pressure where coexist 2 phases
What is relationship between chemical potentials in ohase boundary line
μ(α)=μ(β)
Are infinitesimal changes of chemical potential equal?
Yes
What formula do we get from equation of equality infinitesimal chemical potential changes
ΔSmdT=ΔVmdp
How does Clapeyron equation go
dp/dT=ΔSm/ΔVm=(ΔHm/T)/ΔVm
What is formula if there is melting equilibrium
p-p0=ΔSm/ΔVm(T-T0)
What is sign of melting slope decided by and what is the most common sign for pure substances,say why and exception
By Vm. Its usually + bc Vm(l)>Vm(s); exception is water bc ice is less dense than liquid water and by that molar volume of ice is bigger
What formula do we get from studying evaporation/sublimation boundary line p(α,β)(T)=p*(T)
ln(p/p0)=-ΔHm/R(1/T-1/T0)
What are 2 different conditions for evaporation process
- For the pure substance only(phase coexistance only occurs when p=p*(T)
- When also other substances are present in the gas phase
Ahat is nature of many component ideal gas
There is no interactions between molecules and each component behaves independently in relation to the others
What is partial pressure of i-th component
pi=niRT/V
What is Dalton law
Total pressure is sum of partial pressures
What is chemical potential for i-th component
μi=μi⊝(T)+RTln(pi/p⊝)
When does equilibrium exist in liquid-vapour relation
When chemical potential of 2 phases are equal
μH2O(I)=μH2O(g)=μH2O⊝(T)+RTIn(pH2O*/p⊝)
When is there equilibrium between water-acqueous vapour
a)if its one component system, when pext=pH2O*
b)pH2O=pH2O* in many component system(partial pressure of acqueous vapour is equal to the vappur pressure pf water in the presence of other gasses)
When does water boil
When pH2O* arrives to the value of external pressure(with rise of T)
What is relative humidity
Its equal to pH2O/PH2O*(T)=function of temperature and its often expressed in percentages. If its not 100% we are in “non equilibrium” condition
