PHYSICAL CHEMISTRY IN BRIEF

CHAP. 3: FUNDAMENTALS OF THERMODYNAMICS [CONTENTS] 100

whereS(T 1 , pst) is the entropy of a substance at a sufficiently low temperatureT 1 , such that

the Debye relation (3.62) holds forT≤T 1

S(T 1 , pst) =n

∫T 1

0

constT^3

T

dT=n

constT 13

3

.

∆S(s)is the entropy change on heating the substance fromT 1 to the normal melting temperature

Tfus,

∆S(s)=

∫Tfus

T 1

Cp(s)(T, pst)

T

dT.

∆fusSis the entropy change on melting

∆fusS=

∆fusH

Tfus

.

∆S(l)is the entropy change on heating a liquid substance from the normal melting temper-

ature to the normal boiling temperature,

∆S(l)=

∫Tvap

Tfus

Cp(l)(T, pst)

T

dT.

∆vapSis the entropy change on boiling

∆vapS=

∆vapH

Tvap

.

∆S(g)is the entropy change of a gaseous substance on its transition from the point (Tvap, pst)

to (T, p)

∆S(g)=

∫T

Tvap

Cp(T, pst)

T

dT−

∫p

pst

(

∂V

∂T

)

p

dp.

S Symbols:The superscripts(s),(l),(g)are used to denote quantities in a solid, liquid and gaseous
phase.

Note: If a substance in the solid state transforms from one crystalline form to another

(e.g. rhombic sulphur→monoclinic sulphur), the entropy change at this phase transition

has to be included in the formula.