6 matterandenergy

Matter and Energy:

Solids and Liquids

Basic Chemistry

Rev. 02/20/03

Physical States Solid

Liquid

Gas

Plasma

Properties of Solids, Liquids and GasesProperty Solid Liquid Gas

Position

Expansion

Shape

Volume

Cmprsblty

Density

Mixing


Position Fixed Limited Random

Expansion

Shape

Volume

Cmprsblty

Density

Mixing



Expansion V. limited V. limited infinite

Shape

Volume

Cmprsblty

Density

Mixing




Shape Definite None None

Volume

Cmprsblty

Density

Mixing





Volume Maintains Maintains Any

Cmprsblty

Density

Mixing






Cmprsblty In-compress Slightly Very

Density

Mixing







Density High High Low

Mixing







Density High High Low

Mixing Xtrmly slow Slow Fast

Phase Changes

What are some phase changes

Solid Liquid

Liquid Solid

Liquid Gas

Gas Liquid

Solid Gas

Gas Solid

melting

freezing

vaporization

condensation

sublimation

deposition

Endothermic / ExothermicProcesses that give off energy are called exothermic.

Processes that absorb energy are called endothermic

Solid Liquid

Liquid Solid

Liquid Gas

Gas Liquid

Solid Gas

Gas Solid

melting

freezing

vaporization

condensation

sublimation

deposition

Endothermic or Exothermic ???

???

???

???

???

???

???

Endothermic

Endothermic

Endothermic

Exothermic

Exothermic

Exothermic

Relate this to weather …

Condensation of water vapor to rain drops gives off heat – exothermic.

Evaporation of water to form water vapor absorbs heat, and cools the surroundings – endothermic.

The formation of snow from water vapor gives off heat – exothermic.

Phase changes and the …transfer of energy

Suppose you put a few drops of alcohol on the back of your hand?

Why does it feel cold?Evaporation is an endothermic

process and absorbs heat from the surroundings, your hand.

Vapor Pressure

Vapor Pressure1. Consider a sealed container with water.

1 2

2. Some of the water evaporates to make water vapor

3

3. Some of the water vapor condenses to make liquid water

Water / water-vapor equilibriumA dynamic equilibrium is established when the rate at which liquid water evaporates into water vapor equals the rate at which water vapor condenses into liquid water.

water

vapor

The pressure of the water vapor varies with the

temperature.

water

vapor

Pressure gauge

23 C

Digital Thermometer

Temp.

Pre

ssur

e

What’s the connection between vapor pressure and

boiling?

Boiling occurs at the temperature where the vapor pressure of the

liquid equals the ambient pressure.

What is the boiling point of water here?

The ambient pressure here is usually less than 700 mm Hg.

Water boils at sea level at 100 C where the ambient pressure is 760 mm Hg.

Look at a vapor pressure table.

Therefore, water must boil between 95 C and 100 C, usually around 97.5

At 100 C the At 100 C the vapor pressure vapor pressure is 760 mm Hgis 760 mm Hg

TemperatureTemperatureCorresponding Corresponding

vapor pressure in vapor pressure in mm Hg (or Torr)mm Hg (or Torr)

Therefore water Therefore water boils at 100 C boils at 100 C when the vapor when the vapor pressure of water pressure of water equals the equals the ambient pressure ambient pressure of 760 mm Hgof 760 mm Hg

Water boils at Water boils at the temperature the temperature where the vapor where the vapor pressure equals pressure equals the ambient the ambient pressure.pressure.

When the When the ambient ambient pressure is 690, pressure is 690, water will boil water will boil at the at the temperature temperature where the vapor where the vapor pressure is 690pressure is 690

Around 97 CAround 97 C

At different pressures …When the ambient pressure is very

low, water can even boil at room temperature.

If the ambient pressure is 17.5 mm Hg…

…water would boil at 20.0 C.

TemperatureTemperature

Corresponding Corresponding vapor pressure in vapor pressure in mm Hg (or Torr)mm Hg (or Torr)

At different pressures …When the pressure is much higher

than normal atmospheric pressure, water can stay liquid at temperatures much higher than the normal boiling point, as in your car radiator.

Heat of Fusion and

Heat of Vaporization

Heat of FusionFuse means “to melt”

The heat of fusion is the heat needed to melt one gram of a substance at the melting point.

The heat of fusion of ice can be found experimentally.

Latent heatSometimes the heat of fusion or

heat of vaporization is called the latent heat, or the latent heat of fusion or vaporization.

Latent heats can use the following symbols: Lf or Hf

Lv or Hv

Suppose you had a hot cup of coffee …

… and you wanted to cool it. You could …

1. Blow on it.2. Stick it in the refrigerator3. Add ice to it.

By adding ice …… you cool the coffee because

the ice melts at 0.0 C,extracting heat from the coffee,

and cooling the coffee.The amount of cooling can be calculated using the

heat of fusion of ice.

Measuring the heat of fusion of ice

Time

Tem

pera

ture

Calorimeter with hot water

Temp. probe

Add ice to calorimeter Ti of hot water

Tf of all water

Add ice

All icemelts

The calculations are based on conservation of energy.

The heat lost by the hot water is equal to the heat gained by the melting ice and the water that comes

from the ice.

iwifusihwhw

gainedlost

Tcm Hm Tcm

Q Q

Solve the equation for Hf

Hfus = heat of fusion hw = “hot water” i = “ice” iw = “ice water” c = 4.18J/gC

Heat lost by hot water as it cools

Heat gained by ice as it melts to make water at 0.0 C

Heat gained by “ice water” as it warms from 0.0 to Tf

Solve for Qf

the heat of fusion

i

iwihwhwf

iwifihwhw

gainedlost

m

Tcm - Tcm H

Tcm Hm Tcm

Q Q

Heat of fusion data1. Mass of calorimeter cup2. Mass of cal cup and hot water3. Mass of hot water4. Initial temperature of hot water5. Final temperature of all water6. Mass of cal cup and all water7. Mass of ice added

Procedure1. Heat up water on hot plate2. Set up computer, load calibration file3. Set up “Graph in real time” parameters4. Mass calorimeter cup5. Add hot water and mass cup6. Get baseline temp. of hot water (~ 45 s)

7. Add ice – monitor temp – get Ti and Tf

from “Plot graph” and “examine data”8. Mass calorimeter cup and all water

Stop here, do the lab, then come

back.

Heat of fusion

Ice at 0.0 C

Liquid water at 0.0 C

Releases 334 J per gram

Absorbs 334 J per gram

Hf = 334 J /g (80 cal/g)

Melts (fuses)

Freezes

Heat of vaporization

Liquid water at

100. C Releases 2260 J per gram

Absorbs 2260 J per gram

Hv = 2260 J /g (540 cal/g)

Water vapor at 100. C

Vaporizes

Condenses

Sample problem

Find the amount of heat needed to take 20.00 grams of ice at 0.0 C, melt it, heat it up to 100.0 C and completely boil it away at 100.0 C.

Solution – think about it

Ice at 0.0 C melts, which takes 334 J per gram,


Ice at 0.0 C melts, which takes 334 J per gram, then it heats up to 100.0 which takes 4.18 J per gram per degree,


Ice at 0.0 C melts, which takes 334 J per gram, then it heats up to 100.0 which takes 4.18 J per gram per degree, then the water boils which takes 2260 J per gram.

Solution – formulas and numbers

J 60,240 Q

J/g) g)(2260 (20.00

C) 0J/gC)(100. g)(4.18 (20.00

J/g) g)(334 (20.00 Q

mH Tmc mH Q

tot

tot

vftot

Distillation

Initial ObservationsA clear, colorless liquid has a strong,

alcohol-like odor. When placed on a watch glass and ignited, it burns, but not completely. Some nonflammable liquid remains.

Is the liquid a pure substance?

Is the liquid a mixture?

Heterogeneous or homogeneous?

How could you separate a mixture of two clear,

colorless liquids?

What if the liquids have different boiling points?

What does a “temperature vs time” graph look like for a

single liquid?

Heating curve for a liquid

time

tem

pera

ture

Boiling point of liquid

Temperature hits a plateau as liquid boils

Heating curve for a liquid

time

tem

pera

ture

Boiling point of liquid

Temperature rises when all liquid is vaporized

Heating curve for two liquids, A and B

time

tem

pera

ture

Boiling point of liquid A

Boiling point of liquid B

Fractional distillation can be used to separate the mixture into its various

“factions”.Isolate each fraction at

each of the different boiling points.

Collecting the first fraction

time

tem

pera

ture

12

3

A

B

Collect in the first test tubewhat comes off in region 1.

Collecting the second fraction

time

tem

pera

ture

12

3

A

B

Collect in the second test tube what comes off in region 2.

Collecting the third fraction

time

tem

pera

ture

12

3

A

B

Collect in the third test tubewhat comes off in region 3.

Predict what is in each tube

time

tem

pera

ture

A

B

12

3

Test tube 1 May contain only A

Test tube 2

Test tube 3

May contain both A and B

May contain only B

Equipment setup for doing fractional distillation.

beaker or test tube

thermometer or temperature probe

boiling flask

hot plate

sidearm

Jones condenser

Ring stand and finger clamp

Change the test tube in the beaker to collect each fraction

beaker or test tube

thermometer or temperature probe

boiling flask

hot plate

sidearm

Jones condenser

Ring stand and finger clamp

Test the contents of each test tube for …

1. Odor – does it have an odor? Is it strong or weak?

2. Flammability – does it burn? A lot or a little?

Test by place a small amount on a watch glass and igniting it with a match.

Record your observations

TT#

Start

Temp

End

Temp Odor

Flam-mability

1

2

3

Do the lab and report your

findings to the class.

Phase Diagrams

Phase DiagramsP

ress

ure

Temperature

Vapor pressure

A Phase Diagram of water …P

ress

ure

Temperature

Vapor pressure of

water varies with

temperature

Note negative slope

A Phase Diagram of water …P

ress

ure

760 mm Hg

0.0 C 100.0 C

Where does boiling occur?P

ress

ure

760 mm Hg

100.0 C


ress

ure

234 mm Hg

70.0 C


ress

ure

32 mm Hg

30.0 C


ress

ure

Boiling occurs at the

temperature where the

vapor pressure equals

the ambient pressure.

Which region is which phase?P

ress

ure

Temperature

Solid

LiquidAB

CGas

What are these transitions?P

ress

ure

Temperature

solid

gas

liquid

1

23

45

Transition 1 is …P

ress

ure

Temperature

solid

gas

liquid

1 melting


ress

ure

Temperature

solid

gas

liquid

2

boiling


ress

ure

Temperature

solid

gas

liquid

3

freezing


ress

ure

Temperature

solid

gas

liquid

4sublimation


ress

ure

Temperature

solid

gas

liquid

5

Liquefying a gas by raising the pressure and compressing it

6 matterandenergy

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