J
K
−
1
m
o
l
−
1
We are given that,
△
H
v
a
p
=
42.4
k
J
m
o
l
−
1
,
T
=
273
+
78.4
=
351.4
K
We know that,
△
S
v
a
p
=
△
H
v
a
p
T
putting the values,
=
42.4
×
10
3
351.4
=
120.66
J
K
−
1
m
o
l
−
1
Theory:
Entropy Calculation with phase transformation:
Phase change occurs at constant Pressure & Temperature and is considered reversible if it occurs at its transition temperature.
Entropy change for Vaporisation:
At constant pressure,
q
=
q
p
=
Δ
H
Δ
S
v
a
p
=
Δ
H
v
a
p
T
b
where
T
b
is boiling point of a substance.
