Phase Equilibria Of Pure Substances

Question 1

What is relation between entropy of solid,liquid and gas

Answer 1

Sm(solid)<Sm(liquid)<Sm(gas)

Question 2

What is critical temperature Tc

Answer 2

Above it liquid and gas are no longer estinguishablr andba single fluid exists called superficial fluid

Question 3

What is phase boundary line

Answer 3

Line at certain pressure where coexist 2 phases

Question 4

What is relationship between chemical potentials in ohase boundary line

Answer 4

μ(α)=μ(β)

Question 5

Are infinitesimal changes of chemical potential equal?

Answer 5

Yes

Question 6

What formula do we get from equation of equality infinitesimal chemical potential changes

Answer 6

ΔSmdT=ΔVmdp

Question 7

How does Clapeyron equation go

Answer 7

dp/dT=ΔSm/ΔVm=(ΔHm/T)/ΔVm

Question 8

What is formula if there is melting equilibrium

Answer 8

p-p0=ΔSm/ΔVm(T-T0)

Question 9

What is sign of melting slope decided by and what is the most common sign for pure substances,say why and exception

Answer 9

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

Question 10

What formula do we get from studying evaporation/sublimation boundary line p(α,β)(T)=p*(T)

Answer 10

ln(p/p0)=-ΔHm/R(1/T-1/T0)

Question 11

What are 2 different conditions for evaporation process

Answer 11

1. For the pure substance only(phase coexistance only occurs when p=p*(T)
2. When also other substances are present in the gas phase

Question 12

Ahat is nature of many component ideal gas

Answer 12

There is no interactions between molecules and each component behaves independently in relation to the others

Question 13

What is partial pressure of i-th component

Answer 13

pi=niRT/V

Question 14

What is Dalton law

Answer 14

Total pressure is sum of partial pressures

Question 15

What is chemical potential for i-th component

Answer 15

μi=μi⊝(T)+RTln(pi/p⊝)

Question 16

When does equilibrium exist in liquid-vapour relation

Answer 16

When chemical potential of 2 phases are equal
μH2O(I)=μH2O(g)=μH2O⊝(T)+RTIn(pH2O*/p⊝)

Question 17

When is there equilibrium between water-acqueous vapour

Answer 17

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)

Question 18

When does water boil

Answer 18

When pH2O* arrives to the value of external pressure(with rise of T)

Question 19

What is relative humidity

Answer 19

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