4.1 Basic Concepts and Formulae 249
Coefficient of diffusion (D)
D=
η
ρ(4.13)
Clausius Clepeyron equation
dP
dT=
L
T(ν 2 −ν 1 )(4.14)
whereν 1 andν 2 are the initial and final specific volumes (volume per unit mass) and
Lis the latent heat.
Vander Waal’s equation
(
P+a
V^2)
(V−b)=RT (for one mole of gas) (4.15)The Stefan-Boltzmann law
E=σT^4 (4.16)If a blackbody at absolute temperatureTbe surrounded by another blackbody at
absolute temperatureT 0 , the amount of energyElost per second per square metre
of the former is
E=σ(T^4 −T 04 ) (4.17)whereσ= 5. 67 × 10 −^8 W/m^2 .K^4 is known as Stefan-Boltzmann constant.
Maxwell’s thermodynamic relations
First relation:(
∂S
∂V
)
T=
(
∂P
∂T
)
V(4.18)
Second relation:(
∂S
∂P
)
T=−
(
∂V
∂T
)
P(4.19)
Third relation:(
∂T
∂V
)
S=−
(
∂P
∂S
)
V(4.20)
Fourth relation:(
∂T
∂P
)
S=
(
∂V
∂S
)
P