5 THERMOCHEMISTRY

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222  WITH THE EXCEPTION OF ENERGY FROM _{WITH THE EXCEPTION OF ENERGY FROM}

THE SUN, MOST OF THE ENERGY USED IN THE SUN, MOST OF THE ENERGY USED IN

OUR DAILY LIVES COMES FROM CHEMICAL OUR DAILY LIVES COMES FROM CHEMICAL

REACTIONS. REACTIONS.

 _{THE COMBUSTION OF GASOLINE,}_{THE COMBUSTION OF GASOLINE,}

ELECTRICITY FROM COAL, BATTERIES, ELECTRICITY FROM COAL, BATTERIES,

AND PHOTOSYNTHESIS TO NAME A FEW. AND PHOTOSYNTHESIS TO NAME A FEW.

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333

 THERMODYNAMICS: THE STUDY OF _{THERMODYNAMICS: THE STUDY OF}

ENERGY AND ITS TRANSFORMATIONS.

 _{IN THIS CHAPTER, WE WILL EXAMINE}_{IN THIS CHAPTER, WE WILL EXAMINE} THE RELATIONSHIPS BETWEEN

THE RELATIONSHIPS BETWEEN

CHEMICAL REACTIONS AND ENERGY

CHANGES THAT INVOLVE HEAT, A

PORTION OF THERMODYNAMICS

CALLED THERMOCHEMISTRY.

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444  ENERGY_ENERGY: THE CAPACITY TO DO WORK _{: THE CAPACITY TO DO WORK}

OR TRANSFER HEAT. OR TRANSFER HEAT.

 WORK:_WORK: THE ENERGY USED TO CAUSE AN _{THE ENERGY USED TO CAUSE AN}

OBJECT TO MOVE AGAINST A FORCE. OBJECT TO MOVE AGAINST A FORCE.

 HEAT_HEAT: THE ENERGY USED TO CAUSE _{: THE ENERGY USED TO CAUSE}

THE TEMPERATURE OF AN OBJECT TO THE TEMPERATURE OF AN OBJECT TO

INCREASE. INCREASE.

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777  KINETIC ENERGY_{KINETIC ENERGY}: THE ENERGY OF _{: THE ENERGY OF}

MOTION.

 THE MAGNITUDE OF THE KINETIC _{THE MAGNITUDE OF THE KINETIC}

ENERGY, E

ENERGY, E_k_k, OF AN OBJECT DEPENDS , OF AN OBJECT DEPENDS ON ITS MASS, m, AND SPEED, v.

ON ITS MASS, m, AND SPEED, v.

 EE_k_k = ½ mv = ½ mv22

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 IN CHEMISTRY, WE ARE INTERESTED _{IN CHEMISTRY, WE ARE INTERESTED} IN THE KINETIC ENERGY OF ATOMS

IN THE KINETIC ENERGY OF ATOMS

AND MOLECULES. ALTHOUGH TOO

SMALL TO BE SEEN, THESE

PARTICLES HAVE MASS AND ARE IN

MOTION AND, THEREFORE,

POSSESS KINETIC ENERGY.

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 ALL OTHER KINDS OF ENERGY, LIKE _{ALL OTHER KINDS OF ENERGY, LIKE} THE ENERGY STORED IN A

THE ENERGY STORED IN A

CHEMICAL BOND, HAS

CHEMICAL BOND, HAS POTENTIAL POTENTIAL ENERGY

ENERGY BY VIRTUE OF ITS POSITION BY VIRTUE OF ITS POSITION RELATIVE TO OTHER OBJECTS.

RELATIVE TO OTHER OBJECTS.

POTENTIAL ENERGY IS STORED

ENERGY.

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12 12 12  THE _THESI UNIT _{SI UNIT}FOR ENERGY IS THE_{FOR ENERGY IS THE}

JOULE (J).

 BECAUSE A JOULE IS NOT A LARGE _{BECAUSE A JOULE IS NOT A LARGE}

AMOUNT OF ENERGY, WE OFTEN USE

KILOJOULES (kJ)

KILOJOULES (kJ) IN DISCUSSING THE IN DISCUSSING THE ENERGIES ASSOCIATED WITH

ENERGIES ASSOCIATED WITH

CHEMICAL REACTIONS.

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 A calorie (c) SMALL “c”, IS AN INFORMAL _{A calorie (c) SMALL “c”, IS AN INFORMAL}

NON-SI UNIT USED FOR HEAT

ENERGY.

 A calorie (cal) IS DEFINED AS THE _{A calorie (cal) IS DEFINED AS THE}

AMOUNT OF ENERGY REQUIRED TO

RAISE THE TEMPERATURE OF ONE

GRAM OF WATER BY ONE DEGREE

CELSIUS.

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 A calorie (cal) IS NOW DEFINED IN _{A calorie (cal) IS NOW DEFINED IN} TERMS OF THE JOULE.

TERMS OF THE JOULE.

 1 cal = 4.184 J_{1 cal = 4.184 J}

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 A RELATED ENERGY UNIT IN _{A RELATED ENERGY UNIT IN}

NUTRITION IS THE NUTRITIONAL

C

CALORIE (NOTE THE CAPITOL “C”) ALORIE (NOTE THE CAPITOL “C”)

 1 CAL = 1000 cal = 1 kcal_{1 CAL = 1000 cal = 1 kcal}

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 THE PORTION WE SINGLE OUT FOR _{THE PORTION WE SINGLE OUT FOR} STUDY IS CALLED THE

STUDY IS CALLED THE SYSTEMSYSTEM; ;

EVERYTHING ELSE IS CALLED THE

SURROUNDINGS

SURROUNDINGS. .

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 WHEN WE STUDY THE ENERGY _{WHEN WE STUDY THE ENERGY}

CHANGE OF A CHEMICAL REACTION,

THE

THE REACTANTSREACTANTS AND AND PRODUCTSPRODUCTS ARE THE

ARE THE SYSTEMSYSTEM. THE CONTAINER . THE CONTAINER AND EVERYTHING ELSE BEYOND IT

AND EVERYTHING ELSE BEYOND IT

ARE THE SURROUNDINGS.

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 THE _THEFIRST LAW OF _{FIRST LAW OF}

THERMODYNAMICS

THERMODYNAMICS, ALSO CALLED , ALSO CALLED THE LAW OF CONSERVATION OF

THE LAW OF CONSERVATION OF

ENERGY, STATES THAT ENERGY IS

CONSERVED. THE ENERGY OF THE

UNIVERSE IS CONSTANT. ENERGY

CAN NIETHER BE CREATED OR

DESTROYED, BUT IT CAN BE

CHANGED TO OTHER FORMS.

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 ENDOTHERMIC:_ENDOTHERMIC: A PROCESS _{A PROCESS}

OCCURS IN WHICH THE SYSTEM

ABSORBS HEAT. DURING AN

ENDOTHERMIC PROCESS, SUCH AS

THE MELTING OF ICE, HEAT FLOWS

INTO THE SYSTEM.

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 A PROCESS IN WHICH A SYSTEM _{A PROCESS IN WHICH A SYSTEM} LOSES HEAT IS CALLED

LOSES HEAT IS CALLED

EXOTHERMIC

EXOTHERMIC. DURING AN . DURING AN

EXOTHERMIC PROCESS, SUCH AS

THE COMBUSTION OF GASOLINE,

HEAT EXITS OR FLOWS OUT OF THE

SYSTEM INTO THE SURROUNDINGS.

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 EVERY CHEMICAL REACTION AND _{EVERY CHEMICAL REACTION AND} CHANGE IN PHYSICAL STATE

CHANGE IN PHYSICAL STATE

RELEASES OR ABSORBS HEAT.

 _{REMEMBER EXOTHERMIC (ENERGY}_{REMEMBER EXOTHERMIC (ENERGY} RELEASED) AND ENDOTHERMIC

RELEASED) AND ENDOTHERMIC

(ENERGY ABSORBED)

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 WHEN YOU REMOVE THE PLASTIC _{WHEN YOU REMOVE THE PLASTIC} WRAP FROM A HEAT PACK/HAND

WRAP FROM A HEAT PACK/HAND

WARMER, OXYGEN ENTERS THE

PACK AND REACTS WITH IRON IN

THE PACK IN AN EXOTHERMIC

REACTION.

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 THIS IS REPRESENTED BY THE _{THIS IS REPRESENTED BY THE} FOLLOWING EQUATION:

FOLLOWING EQUATION:

 4Fe + 3O4Fe + 3O₂₂ YIELDS 2Fe YIELDS 2Fe₂₂OO₃₃ + 1625 kJ + 1625 kJ

 ENERGY IS SHOWN AS A PRODUCT _{ENERGY IS SHOWN AS A PRODUCT} OF THE REACTION, WHICH MEANS

OF THE REACTION, WHICH MEANS

HEAT IS RELEASED (EXOTHERMIC)

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 IF YOU DISSOLVE AMMONIUM _{IF YOU DISSOLVE AMMONIUM} NITRATE (NH

NITRATE (NH₄₄NONO₃₃) IN WATER, THE ) IN WATER, THE TEMPERATURE OF THE WATER

TEMPERATURE OF THE WATER

DECREASES. (A COLD PACK)

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 THE EQUATION FOR THIS REACTION _{THE EQUATION FOR THIS REACTION} IS:

IS:

 27 kJ + NH27 kJ + NH₄₄NONO₃₃ YIELDS NH YIELDS NH₄₄++ + NO_{+ NO} 3 3-

- ENERGY IS ON THE REACTANT SIDE _{ENERGY IS ON THE REACTANT SIDE} WHICH MEANS THAT ENERGY IS

WHICH MEANS THAT ENERGY IS

ABSORBED. (ENDOTHERMIC)

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 IN ORDER TO MEASURE AND STUDY _{IN ORDER TO MEASURE AND STUDY} ENERGY CHANGES THAT

ENERGY CHANGES THAT

ACCOMPANY CHEMICAL REACTIONS,

WE NEED TO DEFINE A PROPERTY

CALLED

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 ENTHALPY (H):_{ENTHALPY (H):} THE HEAT CONTENT _{THE HEAT CONTENT} OF A SYSTEM AT CONSTANT

OF A SYSTEM AT CONSTANT

PRESSURE.

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 SPECIFIC HEAT_{SPECIFIC HEAT}: THE SPECIFIC HEAT OF _{: THE SPECIFIC HEAT OF} ANY SUBSTANCE IS THE AMOUNT OF

ANY SUBSTANCE IS THE AMOUNT OF

HEAT REQUIRED TO RAISE THE

TEMPERATURE OF ONE GRAM OF THAT

SUBSTANCE BY ONE DEGREE CELSIUS.

 DIFFERENT SUBSTANCES HAVE _{DIFFERENT SUBSTANCES HAVE}

DIFFERENT COMPOSITIONS, EACH

SUBSTANCE HAS ITS OWN SPECIFIC

HEAT.

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35 35 35 35  WATER HAS A SPECIFIC HEAT OF 4.184 J, _{WATER HAS A SPECIFIC HEAT OF 4.184 J,}

ETHANOL 2.44, IRON 0.449, AND GOLD 0.129.

 IF THE TEMPERATURE OF WATER IS TO _{IF THE TEMPERATURE OF WATER IS TO} RISE BY ONE DEGREE, 4.184 J MUST BE

RISE BY ONE DEGREE, 4.184 J MUST BE

ABSORBED BY EACH GRAM OF WATER.

 ONLY 0.129 J IS REQUIRED TO RAISE THE _{ONLY 0.129 J IS REQUIRED TO RAISE THE} TEMP OF AN EQUAL AMOUNT OF GOLD BY

TEMP OF AN EQUAL AMOUNT OF GOLD BY

ONE DEGREE.

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 BECAUSE OF ITS HIGH SPECIFIC _{BECAUSE OF ITS HIGH SPECIFIC} HEAT, WATER CAN ABSORB AND

HEAT, WATER CAN ABSORB AND

RELEASE LARGE QUANTITIES OF

HEAT.

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 THE AMOUNT OF ENERGY _{THE AMOUNT OF ENERGY}

ABSORBED OR RELEASED CAN BE

CALCULATED BY THE FORMULA:

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 q = heat absorbed or released_{q = heat absorbed or released}

 _{c = specific heat of substance}_{c = specific heat of substance}

 m = mass of sample in grams_{m = mass of sample in grams}

 _{^T = final temp.}_{^T = final temp.}

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40 40 40 40  GIVEN THE FOLLOWING INFO:_{GIVEN THE FOLLOWING INFO:}

 A 5 g PIECE OF LEAD AT 85_{A 5 g PIECE OF LEAD AT 85}00 CELSIUS AND _{CELSIUS AND}

A SPECIFIC HEAT OF 0.129 J. A SPECIFIC HEAT OF 0.129 J.

 A 5 g PIECE OF ALUMINUM AT 65_{A 5 g PIECE OF ALUMINUM AT 65}00 CELSIUS _CELSIUS

AND A SPECIFIC HEAT OF 0.897 J. AND A SPECIFIC HEAT OF 0.897 J.

 THERMAL EQUILIBRIUM OF THE TWO _{THERMAL EQUILIBRIUM OF THE TWO}

METALS EQUALS 25

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

A) CALCULATE “q” FOR EACH

_{A) CALCULATE “q” FOR EACH}

METAL.



B) WHICH METAL LOSES MORE

_{B) WHICH METAL LOSES MORE}

HEAT?

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42 42 42 42  GIVEN THE FOLLOWING:_{GIVEN THE FOLLOWING:}

 A pond made of 14,500 kg of granite rock _{A pond made of 14,500 kg of granite rock}

contains 22,500 kg of water. The specific heat contains 22,500 kg of water. The specific heat

of water is 4.184 J . The specific heat of granite of water is 4.184 J . The specific heat of granite

is 0.803 J. The change in temp for both is 22 is 0.803 J. The change in temp for both is 2200

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

22,500 kg of water is 2.25 x 10

_{22,500 kg of water is 2.25 x 10}

77

g

_g



14,500 kg of granite is 1.45 x 10

_{14,500 kg of granite is 1.45 x 10}

77

g.

_g.

 Because each substance has its own _{Because each substance has its own}

specific heat, the amount of heat absorbed

and released are calculated separately.

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

The specific heat of ethanol is

_{The specific heat of ethanol is}

2.44 J. If the temperature of 34.4

g of ethanol increases from 25

00

C to 78.8

00

C, how much heat has

been absorbed by the ethanol?

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

The temperature of a sample of

_{The temperature of a sample of}

iron with a mass of 10g changed

from 50.4

00

C to 25.0

_{C to 25.0}

00

C with the

_{C with the}

release of 114 J heat. What is

the specific heat of iron?

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 HEAT CHANGES THAT OCCUR DURING _{HEAT CHANGES THAT OCCUR DURING} CHEMICAL AND PHYSICAL PROCESSES

CHEMICAL AND PHYSICAL PROCESSES

CAN BE MEASURED ACCURATELY

USING A CALORIMETER.

 CALORIMETER_CALORIMETER: INSULATED DEVICE _{: INSULATED DEVICE} USED FOR MEASURING THE AMOUNT

USED FOR MEASURING THE AMOUNT

OF HEAT ABSORBED OR RELEASED

DURING A CHEMICAL/PHYSICAL

PROCESS.

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