CHE142 - Assignment : E-book On Phase Diagram (2014)

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E-BOOK ON PHASE DIAGRAM

Prepared By:-

Name Matrix Number

Prepared For:-

Date of Submission:- 22ND SEPTEMBER 2014

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TABLE OF CONTENT

Bil Title Page

1. Cover Page 1

2. Table of Content 2

3. Definition Phase Component System Gibb’s Phase Rule

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4. Phase Diagram One Component System

H2O system

Two Component System Characteristic of Ideal & Non-Ideal

Solution Ideal Solution

Vapour-Pressure Composition Diagram

Temperature Composition Diagram

Distillation of Ideal Solution Non-Ideal Solution

Types of Deviations

Vapour-Pressure Composition Diagram

Temperature Composition Diagram

5 6 7 7 8 8 8 8 9 9 9 9

5. References 10

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DEFINITION OF PHASE, SYSTEM, COMPONENT & PHASE RULE

Phase

Any of the forms or states, solid, liquid,

gas, or plasma, in which matter can exist,

depending on temperature and pressure.

A discrete homogeneous part of a material

system that is mechanically separable

from the rest, as is ice from water.

Component

One of the minimim number of chemically distinct constituents necessary to

describe fully the composition of each phase in a system.

System

An integrated whole , composed of diversed, interacting, specialized structures

and sub functions.

An integrated structure of components and subsystems capable of performing, in

aggregate , one or more specific functions,

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The phase rule describes the possible number of degrees of freedom in a closed

system at equilibrium, in terms of the number of separate phases and the number

of chemical constituents in the system.

GIBB’S PHASE RULE :

The Degrees of Freedom

( F )

the number of independent intensive variables (i.e.

those that are independent of the quantity of material

present) that need to be specified in value to fully

determine the state of the system. Typical such

variables might be temperature, pressure, or

concentration

A Phase

( P )

a component part of the system that is immiscible with

the other parts (e.g. solid, liquid, or gas); a phase may

of course contain several chemical constituents, which

may or may not be shared with other phases. The

number of phases is represented in the relation by P

The Chemical Constituents

( C )

The distinct compounds (or elements) involved in the

equations of the system. (If some of the system

constituents remain in equilibrium with each other

whatever the state of the system, they should be

counted as a single constituent.) The number of these

is represented as C.

.

F = C – P +2

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PHASE DIAGRAM

Phase diagram is graphical representation of the physical states of a substance

under different conditions of temperature and pressure. A typical phase diagram has

pressure on the y-axis and temperature on the x-axis. As we cross the lines or curves on

the phase diagram, a phase change occurs. In addition, two states of the substance

coexist in equilibrium on the lines or curves.

Phase Diagram of One-Component System

Figure 1 , General Phase Diagram

Triple point The point on a phase diagram at which the three

states of matter ; gas, liquid and solid coexist.

Critical point The point on a phase diagram at which the substance

is distinguishable between liquid and gaseous states.

Fusion ( Melting or Freezing )

curve

The curve on a phase diagram which represents the

transition between liquid and solid states.

Vaporization ( or

Condensation) curve

The curve on a phase diagram which represents the

transition between gaseous and liquid states.

Sublimation ( or deposition )

curve

The curve on a phase diagram which represents the

transition between gaseous and solid states.

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Most pure compound have the phase diagram that the solid-liquid slopes forwards

except for water and bismuth. Phase Diagrams for a pure compound such as phase

diagrams for water (H2O) and carbon dioxide (CO2) are phase diagrams for a single

component system.

Phase Diagram of Water, H2O

1) The solid-liquid slopes backwards

rather than forwards.

2) The melting point gets lower at high

temperature because ice is less

dense than water, so when it melts,

the water formed occupies a smaller

volume.

3) The green arrow in the phase

diagram shows that the water would

first freeze to form ice as it crosses

into the solid area and when the

pressure fell low enough the ice

would then sublime to give water

vapour. ( liquid → solid → vapour )

For all substances, density changes with temperature. The mass of material does

not change, but the volume or space that it occupies either increases or decreases with

temperature. The vibration of molecules increases as temperature rises and they absorb

more energy. For most substances, this increases the space between molecules, making

warmer liquids less dense than cooler solids. However, this effect is offset in water by

hydrogen bonding. In liquid water, hydrogen bonds connect each water molecule to

approximately 3.4 other water molecules. When water freezes into ice, it crystallizes into

a rigid lattice that increases the space between molecules, with each molecule hydrogen

bonded to 4 other molecules.

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Phase Diagram of Two Component System

Characteristic of An Ideal Solution & Non-Ideal Solution :-

aA + bB → cC +dD

Characteristic of An Ideal Solution Characteristic of A Non-Ideal Solution

1. Intermolecular forces of attraction A-A,

B-B & A-B are equal.

1. Intermolecular forces of attraction A-A,

B-B & A-B vary.

2. No energy changes in the formation of

the solution, ∆Hsolution = 0 .

2. There is energy changes in the

formation of the solution, ∆Hsolution ≠ 0 .

3. Volume of the solution equal to the

sum of the volume of the 2 liquids A

and B, ∆Vsolution = 0 .

3. Volume of the solution different from

the sum of the volume of the 2 liquids

A and B, ∆Vsolution ≠ 0 .

4. Obeys the Raoult’s Law. 4. Does not obey the Raoult’s Law.

5. Vapour-Pressure equal as predicted

by Raoult’s Law, Pactual = Ppredicted .

5. Vapour-Pressure not equal as

predicted by Raoult’s Law, Pactual ≠

Ppredicted .

There are 2 main types of composition diagrams – pressure and temperature. This is an

example of how the total vapor pressure changes for an ideal solution:-

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Ideal Solution

Pressure Composition Diagram Explanation

The vapor phase is enriched in the more

volatile component. The relationship is not

exactly linear. The line labeled a-b is called

a “tie line”. It connects the liquid and

gaseous phases that are in equilibrium.

Temperature Composition Diagram Explanation

The temperature/composition diagram is

the type we have found in lab. The tie line

connects the composition of the vapor and

liquid phases at a given temp.

Distillation of Ideal Solution

The temp/composition diagram shows how

you can separate 2 liquids with different boiling points.

The number of simple distillations needed to separate

2 liquids is called the number of theoretical plates for

the fractional distillations. Again these solutions show

“ideal solution” behavior.

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Non-Ideal Solution

Azeotropes : Non-Ideal Solution Behaviour

Pressure Composition Diagram Explanation

This diagram shows a low boiling

azeotrope. This composition boils at a

lower temp than the pure liquids. The

interactions increase the VP and

destabilizes the liquid. At the azeotrope pt.

the vapor and liquid have the same

composition and separation cannot be

effected without adding a 3rd component.

Temperature Composition Diagram Explanation

In this situation we have a high boiling

azeotrope. This composition boils at a

higher temperature than the pure liquids.

The interactions reduce the VP and

stabilizes the liquid. At the azeotrope pt.

the vapor and liquid have the same

composition and separation cannot be

effected without adding a 3rd component.

Types of Deviation

Solute-solvent attractions are

weaker than the solute-solute and

solvent-solvent attractions.

A-A, B-B > A-B

Ptotal (actual) > Ptotal (predicted)

Volume increases , ∆H = positve

Solute-solvent attractions are

stronger than the solute-solute and

solvent-solvent attractions.

A-A, B-B < A-B

Ptotal (actual) < Ptotal (predicted)

Volume decreases , ∆H = negative

Positive Deviation Negative Deviation

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REFERENCES

BOOKS

1. Kotz, John C., and Paul Jr. Treichel. Chemistry & Chemical Reactivity. N.p.:

Saunders College Publishing, 1999.

2. Oxtoby, David W., H. P. Gillis, and Alan Campion. Principles of Modern

Chemistry. Belmont, CA: Thomson Brooks/Cole, 2008.

3. Petrucci, Ralph, and William Harwood. F. Geoffrey Herring. Jeffry Madura.

General Chemistry: Principles and Modern Applications. 9th ed. Upper Saddle

River, NJ: Pearson, 2007.

WEBSITES

1. http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/P

hases_of_Matter/Phase_Transitions/Phase_Diagrams.

2. http://en.wikipedia.org/wiki/Phase_rule

3. http://www.chemguide.co.uk/physical/phaseeqia/phasediags.html

4. http://gibbs.uio.no/phase_rule.html