1

Hot Packs and Cold Packs• Common Medical “Over the Counter” products

– “Universals” use mechanical heat storage• Put in freezer or microwave, then to injury• Temporary use, but can be recycled

– “Instant” packs involve chemical reactions• Exothermic and Endothermic chemistry• Usually single-use, but no pre-heating or cooling required• We will explore these chemical types in today’s experiment

2

Thermal Semantics• Temperature

– A quantitative measure of “hot and cold”• Arbitrary scales; Fahrenheit, Centigrade, Kelvin• An indicator of kinetic energy content

– Does not depend on amount of material• Ocean & tea cup can have same temperature

• Heat– A quantitative measure of energy transfer

• Measured in Joules or Calories• Energy flows from hot to cold spontaneously• Transfer by conduction or radiation

– Depends on amount of material involved• More material involves more heat transfer• Ocean has more heat than a tea cup of water

Temperatures around the Worldleft picture refers to January temperaturesHeat energy is delivered by solar radiation

Temperature difference is a result of unequal heat delivery

3

Global Temperature HistoryShort term “warming”, but long term trend is “cooling”

Global WarmingCurrent trend began >10k years ago, are we now “between glacial periods”?

66

Changes in Energy• Heat Energy change requires definitions

– Viewpoint is perspective of system changing• Negative Energy considered as LOSS

– Heat flowing OUT OF a fireplace or oven– Oven loses heat when oven door opens

• Positive Energy viewed as net GAIN– Heat flows INTO an ice cube to melt it– Kitchen warms due to open oven door

– Energy change is algebraic difference• Definition: E after – E before = ΔE change

• Depends only on the initial and ending conditions– NOT dependent on the path taken– Ice sample could be melted 10 times and frozen 9

» Same result as melted once

7

James Joule experimentdemonstrated equivalence of potential energy and heat

88

Energy (Enthalpy) of Thermal Change

• “Enthalpy” or ∆H indicates Thermal energy• Thermal Changes due to Chemical Reactions

– Exothermic reaction = heat generated• Enthalpy sign is NEGATIVE (heat flowing away from system)

– Thermite reaction, neutralization

– burning gasoline, fireplace, hot tub

– body heat from food, rubbing hands to keep warm

– Endothermic reaction = heat absorbed• Enthalpy sign is POSITIVE (heat flows intointo the system)

– Melting Ice, frozen foods

– Evaporation of water & other liquids absorb heat

– Cold can of soda warming on counter

– Choice of direction was arbitrary (like electron charge)• Might not be intuitive, but consistent with other definitions

99

ThermodynamicsLosing Energy

• EX OTHERMIC– Reactions which generate and/or lose heat– Energy is transferred to surroundings

• Burning leaves, coffee cooling, moving automobile

– ΔH or “Enthalpy” is term for heat transfer• -ΔH or “Enthalpy” is negative for Exothermic• (-) Enthalpy becomes part of chemical equation• Enthalpy usually in kJ per Mole• Total energy depends on total quantity

10

EXOthermic reaction (-ΔH) Producing heat or thermal energy by burning fuel,

converting chemical (or nuclear) into kinetic or heat energy

1111

ThermodynamicsGaining energy

• ENDOTHERMIC– Reactions which extract and/or gain heat– Energy is transferred into the object

• Melting ice, coffee being made (water heated)• +ΔH or “Enthalpy” is term for heat input

– ΔH “Enthalpy” positive (+) for Endothermic

• (+) Enthalpy becomes part of chemical equation• Enthalpy usually in kJ per Mole• Total energy depends on total quantity

12

ENDOthermic reaction (+ΔH)Absorbing heat energy from environment

13

Air Conditioning = ENDOthermic cooling results from evaporation reaction absorbing heat

accompanied by exothermic condensation at radiator

1414

1515

Water EnergyMaking water from elements releases heat energy

splitting water into elements requires electrical energy

1616

Bond Energy• Heat results from rearranging chemical bonds

– Reducing available energy (reactants-products) releases energy• Burning wood, animal metabolism

– Increasing chemical energy (products-reactants) absorbs energy• Photosynthesis, melting ice

• Impractical to measure ΔH for every known reaction– Billions of chemical combinations– But use of common bonds provides a practical answer …

• Can use common “features” to divide and conquer– Bond breaking energy can be determined for reference cases

• Carbon-Carbon bonds (single C-C, double C=C, triple C≡C)• Diatomic molecules (Cl2, H2, O2, etc.)

– Use known bond energies to estimate new combinations• Algebraic sum of the bond energy components• Must use balanced equations and appropriate multipliers

17

Sample Bond Energy CalculationBurning of Hydrogen in Air, producing heat

Tables of data differ, but have similar values

18

A few common bond energies

1919

Table of Bond Energies combustion heat output

20

A home furnace exampleWe can predict heat from burning methane via bond energies

• Burning Methane CH4+ 2O2 CO2 + 2H2O• Reactants:

– 4 * C-H bonds x 414kJ/mol * 1mol= 1656kJ– O=O bond = 498kJ/mol * 2mol = 996– Total reactants bond energies = 2652kJ

• Products: – 2 * C=O bonds x 803kJ/mol = 1606kJ– 2 * H-O bonds x 464kJ/mol * 2 mol = 1856kJ– Total products bond energies = 3462 kJ

• Change = 2652 - 3462 = - 810 kJ– Literature value comparison = - 803 to - 889kJ/mole– Negative energy change means ExothermicExothermic– Products more tightly bonded than reactants– Takes more energy to pull products apart– Excess energy released as Heat

2121

Standard State

• Must define “state” of material for reference– Gas, Liquids, Solids have different energy content

• Evaporation of water cools (energy loss 44kJ/mole)• Compression of refrigerant heats it (energy gain)

– “STP” is a definition for reference (standard) state• Reference temperature (typically 0 or 25 degrees Celsius)• 1 atmosphere of pressure• Concentration of 1.00 Moles per Liter (usually)

2222

Heats of reactionsyour home furnace in chemical termsone last step involves the water vapor

Two reactions can be combined (both of these exothermic)Burning of Methane, and condensation of water vapor. A

thermodynamic model of the furnace in your house.

CH4(g) + 2O2(g) CO2(g) + 2 H2O(g) ΔH = - 810kJ/molH2O(g) H2O(aq) a change of state ΔH = - 44 kJ/mol • Evaporation absorbs heat, so condensation yields heat• Stoichiometry requires consistent number of moles2H2O(g) 2H2O(aq) ΔH = - 88 kJoule

2323

Heats of reactionsCan add the equations, molecules AND reaction energy• Net reaction, adding the two:

CH4(g) + 2O2(g) CO2(g) + 2 H2O(g) ΔH = -810 kJoule2H2O(g) 2H2O(aq) ΔH = - 88 kJoule

-----------------------------------------------------------------------------CH4(g) + 2O2(g) CO2(g) + 2 H2O(aq) ΔH = -898kJoule

• Magnitudes of heat energy combine same as for the molecules in a chemical reaction

24

Some mechanisims

25

Mechanism for heat of solution

26

Heat of solution (dissolving)

27

Calorimeter in a cup

28

We will use a simple calorimeterstyrofoam cups for insulationswirling better than stirring

What’s wrong with this picture?(recall James Joule’s experiment)

29

30

Energy Dimensions

• Original definition is “calorie” (small c)– Energy to raise temp.1 gram (1 ml) water 1.0oC– Turned out to be inconveniently small

• Usual quotation in kcal = “Calorie” (big C)– Energy to raise temp 1.00 liter water by 1.0oC– Calories are NOT in S.I. (MKS) dimensions– Commonly used for food products

• SI or ISO unit of energy is “Joule”– 1 watt for one second = 1 Joule– Conversion is 4.184 Joule/calorie– Same thing is 4.184 kJ/kcal = 4.184 kJ/Calorie

31

Our Procedure

• Perform an EXOTHERMIC reaction– CaCl2 dissolving in water produces heat

– Make a plot to determine maximum temp.– Use Q=m*ΔT*c = calories

• C is a constant for water = 1.00

– Calculate kcal per mole• Moles from mass of salt & formula weight• Compare to literature values, how close?

32

Calculations

• Similar to burning of food experiment– Heat is delivered to measured mass of water

• Calories into water + salt, Q = m*c*∆T• Q = heat in calories• M = actual mass of water + salt ( ≈ 120gram)• C = specific heat of water = 1 cal/(gm*∆T)• Q = 120gm*1cal/(gm*∆T)*∆T = calories• If Q positive, solution gets COLD

• If Q negative, solution gets HOT

33

Procedure• Water

– Weigh empty cup and with ≈100mL water– Obtain mass of water in grams

• Salt– Weigh container without & with salt– Obtain mass of salt in grams

• Temperature– take initial temperature of water

• Mix salt and water– Take temp. every 10 seconds for first 3 minutes– Take temp. every 30 seconds for another 2 minutes– Swirl water in cup to mix between readings

• Plot the data

34

HEATING REACTION

Heat from mixing H2O + CaCl2

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

55.0

60.0

0 100 200 300 400

Time in Seconds

Te

mp

era

ture

Ce

nti

gra

de

35

Calculation Procedure• Use graph to determine maximum temperature reached• Calculate calories produced

– (water grams + salt grams) * ΔT = calories

• Calculate energy per mole derived from salt– Calories / moles = energy per mole– Convert to kJ/mole for literature comparison

• Calories / 4.182 = Joules• Joules / 1000 = kJoules

– Compare to literature values• - 82.0 kJ/mole for CaCl2 (exothermic) is customary value• How close did you get ?• Calculate error = (literature-experimental) / literature • Answer *100 = percent error

36

Sample CalculationMin temp 21.00

Max temp 50.00

∆T 29.0empty

cupwith

contentcontent Grams

Water 5 105 91.06

Calcium Chloride 15 35 20.01

Mass of reactants 111.07

Starting Temperature of reactants (from graph data) = 21.0 oCMaximum temperature (from graph data) = 50.0 oC

ΔT = 29.0

Mass of calorimeter contents (grams of water and salt) = 111.070 gramsSpecific heat of reaction product (given value) = 1.000 calories/(oC*gram)

q = m*∆T*Cp (Cp=specific heat) = 3,221 calories

Grams of salt changing water temperature = 20.01 from data above

Formula weight of CaCl2 [40.078+(2*35.45)] = 110.98 gm/mole

Moles of CaCl2 = 0.1803 moles

Calories per mole of CaCl2 = 17,864 calories/mole

Reaction was exothermic (got HOT), so ∆H must be negative = (17,864) calories/mole

conversion factor for calories to Joules = 4.18 Joules/calorie

heat output in Joules/mole = (74,673) Joules/mole

heat output in kJoules/mole = (74.67) kJoules/mole

Literature value for CaCl2 dissolving in water = (82.0) kJoules/mole

deviation from literature value = -8.9% PerCent

37

2nd half of experiment

• Repeat for ENDOTHERMIC reaction– NH4Cl in water absorbs heat

• Measure masses, initial temperature

• Mix and measure temperature changes

• Plot data

• Calc energy absorbed per mole of salt

• Compare to literature value

38

COOLING REACTION

Heat Loss from mixing H2O + NH4Cl

0.0

5.0

10.0

15.0

20.0

25.0

0 100 200 300 400

Time in Seconds

Te

mp

era

ture

Ce

nti

gra

de

39

Endothermic data exampleMin Temp 7.90Max Temp 20.00

∆T -12.1 empty cupwith

contentcontent Grams

Water 5 105 92.40

Ammonium Chloride 15 35 20.02

Mass of reactants 112.42

Starting Temperature of reactants (from graph data) = 20.0 oCMinimum temperature (from graph data) = 7.9 oC

∆t = -12.1 oC

Mass of calorimeter contents (grams of water and salt) = 112.420 gramsSpecific heat of reaction product (given value) = 1.000 calories/(oC*gram)

q = m*∆T*Cp (Cp=specific heat) = -1,360 calories

Grams of salt changing water temperature = 20.02 from data above

Formula weight of NH4Cl [14.007+(4*1.008)+35.45] 53.49 gm/mole

Moles of CaCl2 = 0.3743 moles

Calories per mole of CaCl2 = (3,634) calories/mole

Reaction was exothermic (got COLD), so ∆H must be POSITIVE = 3,634 calories/mole

conversion factor for calories to Joules = 4.18 Joules/calorie

heat output in Joules/mole = 15,192 Joules/mole

heat output in kJoules/mole = 15.19 kJoules/mole

Literature value for CaCl2 dissolving in water = 14.7 kJoules/mole

deviation from literature value = 3.3% PerCent

40

Now you try it

• Report due next week

41

Los Alamos National Laboratory's Periodic Table

Group**

Period 1 IA 1A

18

VIIIA 8A

1 1 H

1.008

2

IIA 2A

13

IIIA 3A

14

IVA 4A

15

VA 5A

16

VIA 6A

17

VIIA 7A

2 He 4.003

2 3

Li 6.941

4 Be 9.012

5 B

10.81

6 C

12.01

7 N

14.01

8 O

16.00

9 F

19.00

10 Ne 20.18

8 9 10

3 11

Na 22.99

12 Mg 24.31

3

IIIB 3B

4

IVB 4B

5

VB 5B

6

VIB 6B

7

VIIB 7B

------- VIII -------

------- 8 -------

11

IB 1B

12

IIB 2B

13 Al 26.98

14 Si

28.09

15 P

30.97

16 S

32.07

17 Cl

35.45

18 Ar 39.95

4 19 K

39.10

20 Ca 40.08

21 Sc 44.96

22 Ti

47.88

23 V

50.94

24 Cr 52.00

25 Mn 54.94

26 Fe 55.85

27 Co 58.47

28 Ni 58.69

29 Cu 63.55

30 Zn 65.39

31 Ga 69.72

32 Ge 72.59

33 As 74.92

34 Se 78.96

35 Br 79.90

36 Kr 83.80

5 37

Rb 85.47

38 Sr

87.62

39 Y

88.91

40 Zr

91.22

41 Nb 92.91

42 Mo 95.94

43 Tc (98)

44 Ru 101.1

45 Rh 102.9

46 Pd 106.4

47 Ag 107.9

48 Cd 112.4

49 In

114.8

50 Sn 118.7

51 Sb 121.8

52 Te 127.6

53 I

126.9

54 Xe 131.3

6 55

Cs 132.9

56 Ba 137.3

57 La* 138.9

72 Hf 178.5

73 Ta 180.9

74 W

183.9

75 Re 186.2

76 Os 190.2

77 Ir

190.2

78 Pt

195.1

79 Au 197.0

80 Hg 200.5

81 Tl

204.4

82 Pb 207.2

83 Bi

209.0

84 Po (210)

85 At (210)

86 Rn (222)

7 87 Fr

(223)

88 Ra (226)

89 Ac~ (227)

104 Rf (257)

105 Db (260)

106 Sg (263)

107 Bh (262)

108 Hs (265)

109 Mt (266)

110 ---

()

111 ---

()

112 ---

()

114 ---

()

116 ---

()

118 ---

()

Lanthanide Series*

58 Ce 140.1

59 Pr

140.9

60 Nd 144.2

61 Pm (147)

62 Sm 150.4

63 Eu 152.0

64 Gd 157.3

65 Tb 158.9

66 Dy 162.5

67 Ho 164.9

68 Er

167.3

69 Tm 168.9

70 Yb 173.0

71 Lu 175.0

4242

Ice melting classic example of entropy increase described in 1862 by Rudolf Clausius

as an increase in the disagregation of the molecules of the body of ice.

43

Calories in the food• Calories delivered into water, Q = m*c*∆T

• Q = heat in calories• M = actual mass of water heated ( ≈ 100gram)• C = specific heat of water = 1 cal/(gm-∆T)• Q = 100gm*1cal/(gm*∆T)*∆T = calories

• Calories into water came from food– Calories transferred / mass of food = cal/gram

• If 0.5 gram food (preburn-postburn) yields 2 kcal• 2 kcal / 0.5 gram = 4 kcal/gram for the food• 1.0 pound (454 gm) of this food yields ≈ 1800 kcal

4444

Carbon FuelsHeat output of fuel results from breaking bonds, releasing energy

• “Heat of Combustion” for carbon fuels (e.g. gasoline, jet fuel)– Called ΔH of combustion, or Combustion Enthalpy

• Source material always contains C and H– Numbers of C & H varies tremendously– Natural products full of variants: linear + branched + ring structures

• Combustion products always contain H2O and CO2

– Sometimes also CO and NOX (N2O, NO, NO2, NO3)– Depends on amount of oxygen available and temperature

• Theoretically possible to calculate heat of combustion for any fuel– Works for simple materials (hydrogen, methane, benzene)– See table for typical values– Not too practical for “real world” bulk materials

• Too many variations and uncertainties with natural products• Dissolved dinosaurs and vegetation don’t yield pure chemical products

4545

Carbon Fuels

• Fuels have 3 entangled physical properties– Density (grams per cm^3)– Molecular Weight (grams per mole)– Combustion Energy (bond breaking)

• Application defines which is “best”– Higher density (liquid) fuels good for Automobiles

• 5 to 11 carbons in gasoline (depends on season)• More moles per gas tank, drive farther between fillings• Diesel fuel more energy than Gasoline, 11-14 carbons

– Low density (gas) fuels good for domestic use• Vapor state fuels (methane, propane) easy to handle• Constant pressure, simple distribution using pipes• Weight and size of delivery system not important

46

Common Fuels

• Burning Hydrogen (proposed by CA)– 1 H-H bond = 436kJ/mol (22.4 Liters or 5.9 gal )

– or 436kJ/gram of H2

• Burning Methane (natural gas)– 4 C-H bond = 1,656kJ/mol, (22.4Liters or 5.9 gal)

– or 1656kJ/mol / 16gm/mol = 106kJ/gm CH4

• Burning Gasoline (octane=C8H18)– 18C-H & 7C-C bond = 7848+2429 =10,277 kJ/mol– Or 10,277kJ/mjol/114g/mol= 90kJ/gram of octane– density = 0.72 gm/mL, 114g/0.72g/mL= 0.16 Liter

4747

ISO Energy Definition

• Units of Energy, definition of Joule

• Auto data– SUV is 4000 lb= 1842kg– Speed of 62mi/hr = 100km/hr= 27.7 m/sec– kg*(m/s)^2= 1842*27.7*27.7 = 1.41E6 W-S

48

• Gasoline efficiency– 18miles/gallon (my Ford Explorer)– 18mi/g/3.84L/g*1.6km/mile 7.4 km/Liter– At 700 gr/Liter, gasoline 10.6 meter/gm– Gasoline energy = 43.6 kJ/gram– Energy expended = 43.6/10.6 = 4.11 kJ/meter

49

50

51

52

53

Energy Unit Conversions

– ISO Definition: 1 Joule ≡ 1 Watt-Second– Units conversion yields 4.184 Joule/calorie– 100 watt device running 1 hour = 36,000 J = 360 kJ

• 100 watts*1 hour*3600 sec/hour = 3.6*10^5 W-s (or Joules)– 360 kJ / 4.18 kJ/kCal = 86 kcal = 86 Cal– One 12 oz can (355ml) Coke Classic = 146 kcal = 146 Cal– 1.7 hour of light bulb use ~ energy in 1 can “Coke Classic”

• Toshiba “Satellite” Laptop, 15V @5A = 75 watts – 75 is 75% of above light bulb example = 2.7*10^5 W-s– 270kJ / 4.18 kJ/kcal = 65 kcal– 2.3 hours laptop energy ~ 1 can of Coke Classic.

– Watt-seconds becoming a commonplace U/M• Direct links between electricity & chemistry U/M• Usual specification units for camera flash

– 50 w-s flash lasts 1/1000 sec, intensity = 50,000 watts !

54

Human Energy• At 2000 kCal / day

– 2.00E6 cal/day * 4.184 j/cal = 8.369E6 J/day• same as 8.369E6 watt-seconds/day• 60sec/min*60min/hr*24hr/day=8.64E4 sec/day• (8.369E6 w-s/day) /(8.64E4 sec/day) = 96.8 watts

– Human energy output ≈ 100 watt light bulb!• 20 watts to keep brain going• 80 watts to keep warm, locomotion, organ function

• Issues for A/C and critical environments• 500 people generate 50kW of heat!• Clean rooms adjust A/C to match number of people• Sleeping together keeps us warm (Penguin movie)

55

END of Mini-Lecture

• Now to the experiment

5656

Carbon FuelsHeat output of fuel results from breaking bonds, releasing energy

• “Heat of Combustion” for carbon fuels (e.g. gasoline, jet fuel)– Called ΔH of combustion, or Combustion Enthalpy

• Source material always contains C and H– Numbers of C & H varies tremendously– Natural products full of variants: linear + branched + ring structures

• Combustion products always contain H2O and CO2

– Sometimes also CO and NOX (N2O, NO, NO2, NO3)– Depends on amount of oxygen available and temperature

• Theoretically possible to calculate heat of combustion for any fuel– Works for simple materials (hydrogen, methane, benzene)– See table for typical values– Not too practical for “real world” bulk materials

• Too many variations and uncertainties with natural products• Dissolved dinosaurs and vegetation don’t yield pure chemical products

5757

Carbon Fuels

• Fuels have 3 entangled physical properties– Density (grams per cm^3)– Molecular Weight (grams per mole)– Combustion Energy (bond breaking)

• Application defines which is “best”– Higher density (liquid) fuels good for Automobiles

• 5 to 11 carbons in gasoline (depends on season)• More moles per gas tank, drive farther between fillings• Diesel fuel more energy than Gasoline, 11-14 carbons

– Low density (gas) fuels good for domestic use• Vapor state fuels (methane, propane) easy to handle• Constant pressure, simple distribution using pipes• Weight and size of delivery system not important

58

Common Fuels

• Burning Hydrogen (proposed by CA)– 1 H-H bond = 436kJ/mol (22.4 Liters or 5.9 gal )

– or 436kJ/gram of H2

• Burning Methane (natural gas)– 4 C-H bond = 1,656kJ/mol, (22.4Liters or 5.9 gal)

– or 1656kJ/mol / 16gm/mol = 106kJ/gm CH4

• Burning Gasoline (octane=C8H18)– 18C-H & 7C-C bond = 7848+2429 =10,277 kJ/mol– Or 10,277kJ/mjol/114g/mol= 90kJ/gram of octane– density = 0.72 gm/mL, 114g/0.72g/mL= 0.16 Liter

5959

ISO Energy Definition

• Units of Energy, definition of Joule

• Auto data– SUV is 4000 lb= 1842kg– Speed of 62mi/hr = 100km/hr= 27.7 m/sec– kg*(m/s)^2= 1842*27.7*27.7 = 1.41E6 W-S

60

• Gasoline efficiency– 18miles/gallon (my Ford Explorer)– 18mi/g/3.84L/g*1.6km/mile 7.4 km/Liter– At 700 gr/Liter, gasoline 10.6 meter/gm– Gasoline energy = 43.6 kJ/gram– Energy expended = 43.6/10.6 = 4.11 kJ/meter

61

62

63

64

65

Energy Unit Conversions

– ISO Definition: 1 Joule ≡ 1 Watt-Second– Units conversion yields 4.184 Joule/calorie– 100 watt device running 1 hour = 36,000 J = 360 kJ

• 100 watts*1 hour*3600 sec/hour = 3.6*10^5 W-s (or Joules)– 360 kJ / 4.18 kJ/kCal = 86 kcal = 86 Cal– One 12 oz can (355ml) Coke Classic = 146 kcal = 146 Cal– 1.7 hour of light bulb use ~ energy in 1 can “Coke Classic”

• Toshiba “Satellite” Laptop, 15V @5A = 75 watts – 75 is 75% of above light bulb example = 2.7*10^5 W-s– 270kJ / 4.18 kJ/kcal = 65 kcal– 2.3 hours laptop energy ~ 1 can of Coke Classic.

– Watt-seconds becoming a commonplace U/M• Direct links between electricity & chemistry U/M• Usual specification units for camera flash

– 50 w-s flash lasts 1/1000 sec, intensity = 50,000 watts !

66

Human Energy• At 2000 kCal / day

– 2.00E6 cal/day * 4.184 j/cal = 8.369E6 J/day• same as 8.369E6 watt-seconds/day• 60sec/min*60min/hr*24hr/day=8.64E4 sec/day• (8.369E6 w-s/day) /(8.64E4 sec/day) = 96.8 watts

– Human energy output ≈ 100 watt light bulb!• 20 watts to keep brain going• 80 watts to keep warm, locomotion, organ function

• Issues for A/C and critical environments• 500 people generate 50kW of heat!• Clean rooms adjust A/C to match number of people• Sleeping together keeps us warm (Penguin movie)