States of Matter

Common States of MatterGases

What do you know about gases?Liquids

What do you know about liquids?Solids

What do you know about solids?States of matter phet

Kinetic Molecular TheoryThe KMT relates the kinetic energy of molecules to states of matter.

Intro to KMT

The Nature of Gases:Kinetic Molecular Theory (KMT)• Kinetic Energy: what is it?• Energy of a moving object: Ek = ½ mv2

• Assumptions of KMT as it applies to gases• Gas particles…1. Have insignificant volume, (≈ 0)

2. Are in constant, random motion3. Collisions are perfectly elastic4. Do not attract or repel one another5. Average Ek is proportional to absolute

temp

Movement of Gas Particles in a Container

Gas Pressure• Pressure = Force/Area:

• P = F/A• Gas pressure is the result of collision of gas

particles with an object. • Why is there no pressure in a vacuum?• It is the sum of the force of collisions per

unit area

Atmospheric PressureAtmospheric pressure is due to the force of atmospheric gases colliding with objects and weight of atmospheric gases.

BarometerMeasures

atmospheric pressure

Invented by Alejandro Torricelli

Patm presses down on the surface, forces Hg up into the tube

Units of PressurePascal (SI unit) PaMillimeters of Hg mmHgAtmosphere atmTorr torrConversion factors @ 25C: Know these!

1 atm = 760 mmHg = 760 torr = 101.3 kPa = 14.7 psi

Converting Between Units of PressureConvert a pressure of 385 mmHg to

kilopascals (kPa)How would you do it?51.3 kPa

Kinetic Energy & Temperature

13.2 The Nature of Liquids

Both liquids and gases are fluids, i.e. they can flow

13.2 The Nature of LiquidsKey difference from gases:Molecules are close enough to have

intermolecular forces of attractionThis is why liquids have a definite volumeBut not close enough to fix them in placeThis is why molecules of liquids can move

past one another (flow)Condensed matter:

Liquids and solids are known as condensed phases of matter

Evaporation

EvaporationVaporization: the conversion of a liquid to a gas or

vaporEvaporation: vaporization occurring at the surface

of a liquidDuring evaporation, molecules of liquid with sufficient

KE “escape” in to the vapor phaseIn a closed container, some molecules that escaped

re-enter into the liquid phase (condense)Eventually and equilibrium is reached where…The rate of evaporation equals the rate of

condensationWhat would happen to the rate of evaporation when a

liquid is heated? Why?

Vapor PressureVapor pressure is a measure of the force exerted by a gas above a liquid.

13.2

States of matter phet

Vapor PressureIn a closed container, as molecules escape

into the vapor phase, pressure buildsThis is vapor pressureAt a certain pressure, the rate of

vaporization equals the rate of condensationThis is an example of “dynamic equilibrium”

Then vapor pressure is constant

Vapor PressureDepends upon the liquidDepends upon temperature

Vapor PressureDepends upon the liquidDepends upon temperature

Boiling PointA liquid boils when the particles

thoughout the liquid have enough KE to vaporize

This occurs when the vapor pressure of the liquid equals the external pressure on the liquid (e.g. atmospheric pressure)

This means that a liquid can boil at different temperatures, depending on the external pressure.

Boiling Point & Normal Boiling Point Normal boiling

point is the boiling temperature when atmospheric pressure (Patm) = 1 atm

What is the normal BP for ethanol?

What is the BP for ethanol at Patm = 600 torr?

13.3 SolidsCrystal Structure

Simple cubicBody centered

cubicFace centered

cubicAllotropesAmorphous solidsGlasses

Some Types of Unit Cells

AllotropesAllotropes are varying forms of an elementExample: oxygen (O2) and ozone (O3)Example: allotropes of carbon

Non-Crystalline SolidsAmorphous solids lack an ordered internal

structure.Examples: rubber, plastic, asphalt, glass

13.4 Changes of StateVaporization/Condensation

Liquid ↔ GasEvaporationBoilingVapor vs. Gas

Melting/FreezingLiquid ↔ SolidSolidification

Sublimation/DepositionSolid ↔ Vapor I2 (s) → I2 (g)

SublimationSolid VaporSublimation occurs

in solids with vapor pressures that exceed atmospheric pressure at or near room temperature.

Depositiono Vapor Solid

Phase DiagramsShow pressure &

temperature at which various states of matter exist for a given substance

Phase equilibrium exists along each line

Normal m.p./b.p.Triple pointCritical pointNote negative slope

for solid-liquidUnique to water

Phase DiagramsA phase diagram is a graph that

gives the conditions of temperature and pressure at which a substance exists as solid, liquid, and gas (vapor).

Lines represent pressures and temperatures at which two phases are in equilibrium