Phase Diagrams: Understanding States of Matter and Phase Changes, Study notes of Solid State Physics

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Phase Diagrams

A phase diagram is used to show the relationship between temperature, pressure and state of matter.

Before moving ahead, let us review some vocabulary and particle diagrams.

Changes of States of Matter

Freezing start as a liquid, end as a solid, slowing particle motion, forming more intermolecular bonds Melting start as a solid, end as a liquid, increasing particle motion, break some intermolecular bonds Condensation start as a gas, end as a liquid, decreasing particle motion, form intermolecular bonds Evaporation/Boiling/Vaporization start as a liquid, end as a gas, increasing particle motion, break intermolecular bonds

http://phet.colorado.edu/en/simulation/states- of-matter

In the flat sections, heat is being removed by the formation of intermolecular bonds.

The flat points are phase changes.

The heat added to the system are being used to break intermolecular bonds.

Phase diagrams are used to show when a specific substance will change its state of matter (alignment of particles and distance between particles).

Every substance has its own phase diagram.

Some are very complex while others are simple.

H 2 O

Steel

Terminology of Phase Diagrams

Normal Boiling Point and Normal Melting Point

Both terms refer to the temperature at which the substance undergoes a phase change at 1atm (or 101kPa, 760mmHg).

(atm, kPa, and mmHg are pressure measurements)

Terminology of Phase Diagrams

Critical Temperature and Critical Pressure

This is the point on the phase diagram above which a liquid is unable to form.

It cannot form because the particles have TOO much kinetic energy to form intermolecular bonds needed for liquids.

What is the critical temperature and

pressure in the phase diagram below?