Post on 18-Dec-2021
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.
States of Matter
Solid: rigid, has definite volume and definite shape Liquid: flows, has definite volume, but takes the shape of the container Gas: flows, no definite volume or shape, shape and volume are determined by container Plasma: atoms are separated into nuclei (neutrons and protons) and electrons, no definite volume or shape
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
Sublimation
Starts as a solid, ends as a gas, increases particle speed, breaks intermolecular bonds
Deposition
Starts as a gas, ends as a solid, decreases particle speed, forms intermolecular bonds
http://phet.colorado.edu/en/simulation/states-of-matter
The flat sections on the graph are the points where a phase change is occurring.
Both states of matter are present at the same time.
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
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.
H2O
CO2
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)
What is the normal melting point and boiling point on the phase diagram below?
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?
Terminology of Phase Diagrams
Triple Point
The triple point is the location on a phase diagram at which all three lines which divide the three states of matter meet.
At this point, all three states of matter may exist at the same time.
What is the pressure and temperature for the triple point on the phase diagram below?
General Reading Information
The lines dividing the three states of matter indicate phase changes.
When a temperature and pressure point are on a line, then both states of matter (which ever are on either side of the line) are present.
1. What phase changes does line A represent?
2. What phase changes does line B represent?
3. What phase changes does line C represent?