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Lecture 3 – September 2, 2008
State Functions and Variables
Perfect Gas Law is an Equation of State, f (p, V, T, n) = 0
p, V, T, and n are then called
state variables
state variables
can be intensive or extensive
intensive variable
- magnitude of the variable does not depend on the size or amount of the
system
extensive variable
- magnitude of the variable does depend on the size or amount of the system
Intensive
Extensive
Temperature (T)
Mass (m)
Pressure (P)
Volume (V)
Dielectric constant (
ε
)
Number of Moles (n)
Density (
ρ
= m/V)
Energy (U)
Molar Mass (M = m/n)
Enthalpy (H)
Molar Volume (
V
= V/n)
Entropy (S)
Isothermal Compressibility
(
κ =
V
-1
(
∂
V/
∂
p)
T
)
Isobaric (C
p
) and Isochoric (C
v
) Heat
Capacities
Expansion Coefficient (
α =
V
-1
(
∂
V/
∂
T)
p
)
Gibbs (G) and Helmholz (A) Free Energies
Molar Quantities
- Extensive quantities divided by the total number of moles in the system are
themselves intensive quantities

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