OB: Practice phase concepts: cooling and heating curves,

phase diagrams, pressure conversions, table H problems.

Take out NEW reference tables.Recycle the old ones NOW.

Draw the Cooling curve for cobalt. On the same graph, draw the heating curve for cadmium. Titles, axis labels and scales, be big.

TempKelvin

Energy added (or removed) at constant rate over time

3200

2400

1600

800

Draw the heating curve for cobalt. On the same graph, draw the cooling curve for cadmium. Titles, axis labels and scales, be big.

TempKelvin

Energy added (or removed) at constant rate over time

3200

2400

1600

800 CobaltBP: 3200 KFP: 1768 K

CadmiumBP: 1040 KFP: 594 K

Why are the flat lines different lengths on every heating curve (and every cooling curve)?

BC represents the melting of ice. It takes for water, 334 Joules of energy to melt one gram of ice from solid to liquid without increasing the temperature. It’s called the heat of fusionFor water: HF = 334 J/gram

DE represents the boiling of water into steam. It takes for water, 2260 Joules of energy to vaporize one gram of water to steam without increasing the temperature. It’s called the heat of vaporizationFor water: HV= 2260 J/gram

The phase change from liquid to gas is MUCH more energetic than melting solid to liquid. For water, it’s nearly 7X more!

A phase diagram shows one substance’s range of phases through temperature and pressures.

Below is the phase diagram for water.

Special Points on this graph:Tm: normal melting point

Tb: normal boiling point

TP: triple point

CP: critical point

Imagine you have two beakers of liquid, one has 500. mL ethanol alcohol and the other has 500. mL of propanone. They are sitting on the desk in front of you. Put a cork into each top.

AIR PRESSURE101.3 kPa

Start pressure inside flasks

the same

Warm up the room to 25⁰C

What is pressure

inside each flask?

Imagine you have two beakers of liquid, one has 500. mL ethanol alcohol and the other has 500. mL of propanone. They are sitting on the desk in front of you. Put a cork into each top.

AIR PRESSURE101.3 kPa

Start pressure inside flasks

the same

25⁰C

Vapor Pressure ethanol @ 25⁰C is about

8 kPa

Vapor pressure propanone @ 25⁰C is about

31 kPa

What if we heat it up to 65⁰C next???

Imagine you have two beakers of liquid, one has 500. mL ethanol alcohol and the other has 500. mL of propanone. They are sitting on the desk in front of you. Put a cork into each top.

AIR PRESSURE101.3 kPa

Start pressure inside flasks

the same

65⁰C

Vapor Pressure ethanol @ 65⁰C is about

60 kPa

Vapor pressure propanone @ 65⁰C is about

135 kPa

KABOOM!

Properties of SOLIDS, LIQUIDS, and GASES Compared

SOLIDSParticles are strongly attracted to each other, other than some vibration there is nearly no movement of the atoms or molecules, they have a rigid or lattice arrangement of the particles, they keep their shapes and volumes, they do not take the shape of their containers. Solids cannot be compressed very much because the particles are very close together.

Because of this most solids have a high density compared to their liquids orgases. When energy or heat is added, the particles will vibrate more, which often makes solids expand when heated. Particles in solids have the lowest kinetic energy. Give solids enough energy (at the proper pressure) and they will vibrate so much that they break apart and turn into ....

LIQUIDSParticles have some attraction to each other but not enough to make them stuck. Liquids flow over themselves, the particles are in constant random motion. Liquids do not have a definite shape which means they take the shape of the container you put them in.

If you spill liquids, the force of gravity spreads them out quite well. The hotter liquids get when you add energy, the faster the particles move, and liquids too expand slightly when heated. Liquids are dense as well, but usually not as dense as solids are. Heat a liquid enough, the particles move so much that they turn into...

GASESThere is virtually no attractive or repulsive force between the particles. The particles move in straight lines and very fast. They collide with other particles all of the time. These collisions will cause gas (or air) pressure. Gases take the shape of the container that you put them in. Any amount of a gas will fill any container that you putit in.

The collisions are considered to be elastic, meaning there is no loss of kinetic energy due to the collisions. Heated gases make the particles move faster and have more collisions, causing expansion if possible, or greater pressures if contained in a definite volume. Gas Particles have the highest kinetic energy. Gases have very low density.

Gas Pressure is measured with different pressure units, all on table A. Let’s add mm Hg now to the new tables.

1.0 atm = 760. mm Hg = 101.3 kPa = 14.7 psi

Today’s pressure is exactly 1.14 atm.

Convert that to mm Hg, and kPa right now…

This slide left

intentionally blank, you know

why…

1.14 atm1

X = 866 mm Hg (3 SF)760. Mm Hg

1.0 atm

1.14 atm

1

101.3 kPa1.0 atm

X = 115 kPa (3 SF)

At any one temperature, say 65°C,ethanonic acid has the lowest vapor pressure, propanone the highest. WHY???

1stEach liquid, these 4 included, at any one temperature will evaporate to a certain degree.

How much this happens is connected first to the temperature, and then, to how strong the inter-molecular attractions the molecules have for each other.

At 65°CPropanone has the lowest intermolecular attraction and therefore the highest vapor pressure.

Ethanoic acid has strong intermolecular attraction, so low vapor pressure.

Put a small note onto your reference tables if you want to now.

Ethanoic acid has the lowest vapor pressure of these four, at any temp. because it has the strongest intermolecular attractions for itself.

Propanone has the highest vapor pressure of these four, at any temperature, because it has the weakest intermolecular attractions for itself.

Heating curve for an unknown substance

BP

in

FP

K

Energy being added at a constant rate over time.

Heating curve for an unknown substance

BP

in

FP

KB

C

D

E

From BC there is no change in temperature.

From DE there is no change in temperature.

Ergo: Kinetic Energy is steady.

Potential Energy must increase there.

Energy being added at a constant rate over time.

PE

PE

Heating curve for an unknown substance

BP

in

FP

KB

C

D

E

From CD there is an increase in temperature.That means Kinetic Energy Increases

too

If kinetic energy is changing, Potential energy is steady (doin’ nutin’)

Energy being added at a constant rate over time.

Temp

KE

Kinetic Energy & Temperature are the same thing, sort of. The greater the KE, the greater the temp.

Lower temp = lower KE

Temp + Kinetic energyare like Michael Jackson’s hand & his glove. What ever one does, so does the other.

The other energy, Potential Energy,is used when there is no change in the kinetic energy. It’s for those phase change times.

If kinetic energy (temp) is changing, potential energy is steady.

In a phase change kinetic energy is steady (so is temp),

then the PE is going up in a heating curve, or the PE is going down in a cooling curve.

Over break, make sure you read through

all the diaries that you missed. Complete all through the phases diary.

In January we begin thermochemistry. It’s a bunch of math, fun labs, and you’ll want to get an amazing tattoo of the formula.

Q = mC∆T