[1] PVT Behavior of Pure Substances

Gibbs Phase Rule

Describes the possible number of degrees of freedom in an enclosed system at equilibrium, in terms of the number of separate phases and the number of chemical constituents in the system.

Degrees of Freedom

No. of independent variables that must be arbitrarily set to fix the intensive state of a system

phase

A ______ is a homogeneous region of matter. At a boundary between different phases,
properties undergo an abrupt change.

0

What is the minimum no. of degrees of freedom for any system?

invariant

When 𝐹 = 0, the system is said to be______

univariant

When 𝐹 = 1, the system is ______

bivariant

When 𝐹 = 2, the system is _______

Intensive property

Doesn’t change with the amount of substance

Extensive Property

Changes depending on amount

sublimation curve, vaporization curve, fusion curve (solid/liquid equil.)

PT diagrams:

1-2: ________

2-C: ________

2-3: ________

1-2 and 2-C

Vapor pressure lines

Critical Point (Pc & Tc)

Highest temperature and pressure where liquid and vapor phases are observable. Invariant.

Triple Point

3 phases coexist at equilibrium

Vertical lines

PT diagrams: changes occurring at constant T

Horizontal lines

PT diagrams: changes occurring at constant P

Dashed Lines

PT diagrams: regions existing at temperatures and pressures above Pc and Tc

Fluid Regions

neither condensation nor vaporization can be initiated

Vapor, Supercritical Fluid

Gas regions:

Vapor

PT diagrams: left of Tc

Supercritical Fluid

PT diagrams: above Tc

PV diagrams

Regions where 2 phases coexist in equilibrium

Dotted Lines

PV diagrams: different temperatures; isotherms

Subcritical temperature

not smooth; 3 segments (T1 & T2)

Horizontal Segment

PV diagrams: represents all possible mixture of liquid and vapor in equilibrium

liquid

100% ____ to the left end

vapor

100% ____ to the right end

Saturated liquid

Represents single-phase liquid at their vaporization (boiling) temperature

Saturated vapor

Represents single-phase vapor at their condensation temperature

saturation pressure

For a specific subcritical isotherm, there is only one value for the _________

Subcooled-liquid region

Left of the liquid curve BC

Superheated-vapor region

right of the saturated vapor curve CD

subcooled

liquid is ____ if its temperature is below the boiling point for a given pressure

superheated

vapor is _____ if its temperature is above the boiling point for a given pressure

Horizontal segments

become progressively shorter aat high temperatures, ultimately reduced to a point at C

indistinguishable

At and beyond Point C, liquid and vapor phases become _______

Quality (x)

Combination of liquid and vapor

Subcooled liquid

T < Tsat

Saturated liquid, mixture, vapor

Psat, T = Tsat

Superheated vapor

T > Tsat

Q = M - M_L / M_V - M_L

Formula for quality (x)

M = M_L + X (M_V - M_L)

Formula for M, wherein M can be any thermodynamic property

Saturated liquid

x = 0

saturated mixture

0 < x < 1

saturated vapor

x = 1