CHAPTER 17: Heat vs. Temperature - pkwy.k12.mo.us · PDF fileCHAPTER 17: THERMOCHEMISTRY Page 504 – 539 Heat vs. Temperature ATOM ... Rates of Reaction The heat given off by the

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CHAPTER 17: THERMOCHEMISTRY

Page 504 – 539

Heat vs. TemperatureHeat vs. Temperature

�� ATOMATOM�� Heat energy= Kinetic Heat energy= Kinetic

energyenergy

�� SUBSTANCESUBSTANCE�� Heat energy = TOTAL Heat energy = TOTAL

Kinetic energy of all Kinetic energy of all atoms in a substanceatoms in a substance

�� Temperature = Temperature = AVERAGE Kinetic AVERAGE Kinetic energy of the atoms in energy of the atoms in a substancea substance

�� Each atom contains Each atom contains Kinetic energyKinetic energy�� Like each test has a Like each test has a

scorescore

�� All the energy can be All the energy can be added together = added together = amount of heat amount of heat energyenergy�� Total pointsTotal points

�� The energy can be The energy can be averaged= averaged= temperaturetemperature�� Average of all scoresAverage of all scores

8484AverageAverage

252252Total Total

959533

727222

858511

PointsPointsTestTestHeat vs. TemperatureHeat vs. Temperature

�� HeatHeat�� Units: Joule (J)Units: Joule (J)�� 1KJ = 1000J1KJ = 1000J

�� Units: caloriesUnits: calories�� 1Kcal = 1000cal1Kcal = 1000cal

�� 4.18J = 1cal4.18J = 1cal

�� TemperatureTemperature�� Units: Celsius (Units: Celsius (°°C) or C) or

Kelvin (K)Kelvin (K)�� Kelvin = Kelvin = °°C + 273C + 273

Heat Capacity vs. Specific HeatHeat Capacity vs. Specific Heat

�� Heat Capacity (C)Heat Capacity (C)�� J/J/°°CC

�� Specific Heat (c)Specific Heat (c)�� J/gJ/g··°°CC�� Table page 508Table page 508

�� Water= 4.18J/gWater= 4.18J/g··°°CC�� Water= 1.00cal/g Water= 1.00cal/g ··°°CC

q = mcq = mc∆∆TT

�� q = heat (J)q = heat (J)

�� m = mass (g)m = mass (g)

�� c = specific heat (J/gc = specific heat (J/g··°°C)C)

�� ∆∆T = change in temperature (T = change in temperature (°°C)C)

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ExampleExample

�� The temperature of a 95.4g piece of The temperature of a 95.4g piece of copper increases from 25.0copper increases from 25.0°°C to 48.0C to 48.0°°C C when the copper absorbs 849J of heat. when the copper absorbs 849J of heat. What is the specific heat of copper.What is the specific heat of copper.

�� q=q= m=m= c=c= ∆∆T=T=

�� 849J/95.4g x 23.0849J/95.4g x 23.0°°C = C =

�� 0.387J/g0.387J/g··°°CC

Solving for qSolving for q

�� Find the amount of heat needed to raise Find the amount of heat needed to raise the temperature of 15.0g of water from the temperature of 15.0g of water from 25.0 to 35.025.0 to 35.0°°CC

�� q =q = m= c= m= c= ∆∆T=T=

�� 15.0g x 4.18J/g15.0g x 4.18J/g··°°C x 10.0C x 10.0°°CC

�� q= 627Jq= 627J

Solving for Solving for ∆∆TT

�� How much temperature change would How much temperature change would occur if 627J of heat were added to 15.0g occur if 627J of heat were added to 15.0g of aluminum?of aluminum?

�� Q = m= c= Q = m= c= ∆∆T=T=

�� 627J/15.0g x 0.90J/g627J/15.0g x 0.90J/g··°°CC

�� 46.446.4°°CC

ThermochemicalThermochemical Equations Equations

�� Include the heat change Include the heat change

�� Include the phase of substancesInclude the phase of substances

�� Amount of heat given is for the number of Amount of heat given is for the number of moles of each substance indicated by the moles of each substance indicated by the coefficients in the equationcoefficients in the equation

Why Phase of Substance Why Phase of Substance Must Be Included Must Be Included

�� Decomposition of 1 mole of WaterDecomposition of 1 mole of Water�� HH22OO(l)(l) �� HH2(g)2(g) + + ½½OO2(g)2(g) ∆∆H=285.8KJH=285.8KJ

�� HH22OO(g)(g) �� HH2(g)2(g) + + ½½OO2(g)2(g) ∆∆H=241.8KJH=241.8KJ

difference= 44.0KJdifference= 44.0KJ

�� Difference in Difference in ∆∆H is due to the difference in H is due to the difference in physical statephysical state

�� HH22OO(l)(l) �� HH22OO(g)(g) ∆∆H=44.0KJH=44.0KJ

Exothermic vs. EndothermicExothermic vs. Endothermic

�� ExoExo = out= out

�� Endo = withinEndo = within

�� ThermicThermic = pertaining to heat= pertaining to heat

�� CC(s)(s) + O+ O2(g)2(g) �� COCO2(g)2(g) + 393.5KJ+ 393.5KJ�� Exothermic or EndothermicExothermic or Endothermic

�� 2CuO2CuO(s)(s) + 314.6KJ + 314.6KJ �� 2Cu2Cu(s)(s) + O+ O2(g)2(g)

�� Exothermic or EndothermicExothermic or Endothermic

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Another Way to WriteAnother Way to Write

�� CC(s)(s) + O+ O2(g)2(g) �� COCO2(g)2(g) ∆∆H=H= --393.5KJ393.5KJ�� Negative (Negative (--) ) ∆∆H = heat is given off by the H = heat is given off by the

reactionreaction

�� 2CuO2CuO(s)(s) �� 2Cu2Cu(s)(s) + O+ O2(g) 2(g) ∆∆H =H = +314.6KJ+314.6KJ�� Positive (+) Positive (+) ∆∆H = heat is put into the reactionH = heat is put into the reaction

Standard enthalpy of formation (∆H0) is the heat change that results when one mole of a compound is formed from its elements at a pressure of 1 atm.

f

The standard enthalpy of formation of any element in its most stable form is zero.

∆H0 (O2) = 0f

∆H0 (O3) = 142 kJ/molf

∆H0 (C, graphite) = 0f

∆H0 (C, diamond) = 1.90 kJ/molf

6.6

6.6

Enthalpy Change (Enthalpy Change (∆∆H)H)�� Find the heat change for the burning of Find the heat change for the burning of

25.0g of carbon25.0g of carbon�� 11--balanced chemical equationbalanced chemical equation

•• CC(s)(s) + O+ O2(g)2(g) �� COCO2(g)2(g) + 393.5KJ+ 393.5KJ

�� 22--given over 1given over 1•• 25.0g C/125.0g C/1

�� 33--check to see if given is in moles if not check to see if given is in moles if not convert to molesconvert to moles•• 25.0g25.0g

�� 44--Use mole to energy ratioUse mole to energy ratio

The standard enthalpy of reaction (∆H0 ) is the enthalpy of a reaction carried out at 1 atm.

rxn

aA + bB cC + dD

∆H0rxn d∆H0 (D)fc∆H0 (C)f= [ + ] - b∆H0 (B)fa∆H0 (A)f[ + ]

∆H0rxn ∆H0 (products)f= Σ ∆H0 (reactants)fΣ-

6.6

Hess’s Law: When reactants are converted to products, the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps.

(Enthalpy is a state function. It doesn’t matter how you get there, only where you start and end.)

Benzene (C6H6) burns in air to produce carbon dioxide and liquid water. How much heat is released per mole of benzene combusted? The standard enthalpy of formation of benzene is 49.04 kJ/mol.

2C6H6 (l) + 15O2 (g) 12CO2 (g) + 6H2O (l)

∆H0rxn ∆H0 (products)f= Σ ∆H0 (reactants)fΣ-

∆H0rxn 6∆H0 (H2O)f12∆H0 (CO2)f= [ + ] - 2∆H0 (C6H6)f[ ]

∆H0rxn = [ 12 × -393.5 + 6 × -285.8 ] – [ 2 × 49.04 ] = -6535 kJ

-6535 kJ2 mol

= - 3267 kJ/mol C6H6

6.6

4

Chemistry in Action:

Fuel Values of Foods and Other Substances

C6H12O6 (s) + 6O2 (g) 6CO2 (g) + 6H2O (l) ∆H = -2801 kJ/mol

1 cal = 4.184 J

1 Cal = 1000 cal = 4184 J

CALORIMETRYCALORIMETRY

�� Technique to Technique to measure amount of measure amount of heat absorbed or heat absorbed or releasedreleased

�� Calorimeter Calorimeter ––instrument used for instrument used for calorimetrycalorimetry

Heat & Phase ChangesHeat & Phase Changes

�� Heat of Fusion & SolidificationHeat of Fusion & Solidification�� ∆∆HHfusfus = = --∆∆HHsolidsolid

�� HH22OO(s)(s) �� HH22OO(l)(l) ∆∆H = 6.01KJ/molH = 6.01KJ/mol�� HH22OO(l)(l) �� HH22OO(s)(s) ∆∆H = H = --6.01KJ/mol6.01KJ/mol

Heat of Fusion ProblemHeat of Fusion Problem

�� How many grams of ice at 0How many grams of ice at 0°°C will melt if C will melt if 2.25KJ of heat are added?2.25KJ of heat are added?�� 11--given over 1given over 1�� 22--use heat of fusion to convertuse heat of fusion to convert

�� Heat of Vaporization & CondensationHeat of Vaporization & Condensation�� ∆∆HHVapVap = = --∆∆HHcondcond

�� HH22OO(l)(l) �� HH22OO(g)(g) ∆∆H = 40.7KJ/molH = 40.7KJ/mol

�� HH22OO(g)(g) �� HH22OO(l)(l) ∆∆H = H = --40.7KJ/mol40.7KJ/mol

Heat of Vaporization ProblemHeat of Vaporization Problem

�� How much heat (in KJ) is absorbed when How much heat (in KJ) is absorbed when 24.8g H24.8g H22OO(l)(l) at 100at 100°°C and 101.3kPa is C and 101.3kPa is converted to steam at 100converted to steam at 100°°CC

5

What You Need To Know About What You Need To Know About Water Water

�� Molar MassMolar Mass == 18.02g18.02g

�� Boiling Point =Boiling Point = 100.0100.0°°CC

�� Freezing Point=Freezing Point= 0.00.0°°CC

�� Specific Heat=Specific Heat= 4.18J/g4.18J/g··°°C or 1cal/gC or 1cal/g··°°CC

�� Heat of fusion=Heat of fusion= 6.01 KJ/mol6.01 KJ/mol

�� Heat of vaporizationHeat of vaporization 40.7KJ/mol40.7KJ/mol

The enthalpy of solution (∆∆∆∆Hsoln ) is the heat generated or absorbed when a certain amount of solute dissolves in a certain amount of solvent.

∆Hsoln = Hsoln - Hcomponents

6.7

Which substance(s) could be used for melting ice?

Which substance(s) could be used for a cold pack?

Calculating the Enthalpy Change in Calculating the Enthalpy Change in Solution FormationSolution Formation

�� How much heat (in KJ) is released when How much heat (in KJ) is released when 2.500mol 2.500mol NaOHNaOH(s(s)) is dissolved in water?is dissolved in water?

�� List the List the knownsknowns and the unknownand the unknown

�� KnownsKnowns�� ∆∆HHsolnsoln = = --445.1KJ/mol (off table)445.1KJ/mol (off table)�� Amount of Amount of NaOHNaOH(s(s)) dissolved = 2.500moldissolved = 2.500mol

First Law of ThermodynamicsEnergy can be converted from one form to another but energy cannot be created or destroyed.

Second Law of ThermodynamicsThe entropy of the universe increases in a spontaneous process and remains unchanged in an equilibrium process.

∆Suniv = ∆Ssys + ∆Ssurr > 0Spontaneous process:

∆Suniv = ∆Ssys + ∆Ssurr = 0Equilibrium process:

18.4

Rates of ReactionRates of Reaction�� The heat given off by the The heat given off by the

corrosion reaction of an ironcorrosion reaction of an iron--magnesium alloy with salt magnesium alloy with salt water can produce a hot water can produce a hot meal. The rate of reaction is meal. The rate of reaction is increased by adding salt increased by adding salt water, so heat is produced water, so heat is produced rapidly. You will learn some rapidly. You will learn some ways in which the rate of a ways in which the rate of a reaction can be increased.reaction can be increased.

18.1

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18.1

Collision TheoryCollision Theory

�� In chemistry, the rate of chemical change, or In chemistry, the rate of chemical change, or the reaction rate, is usually expressed as the the reaction rate, is usually expressed as the amount of reactant changing per unit time.amount of reactant changing per unit time.

18.1


•• A A raterate is a measure of the speed of any change is a measure of the speed of any change that occurs within an interval of time.that occurs within an interval of time.

Collision TheoryCollision Theory•• Rates of chemical reactions are often measured as Rates of chemical reactions are often measured as

a change in the number of moles during an interval a change in the number of moles during an interval of time.of time.

18.1


•• According to According to collision theorycollision theory , atoms, ions, and , atoms, ions, and molecules can react to form products when they molecules can react to form products when they collide with one another, provided that the colliding collide with one another, provided that the colliding particles have enough kinetic energy.particles have enough kinetic energy.

18.1


•• Effective CollisionEffective Collision

18.1


•• Ineffective CollisionIneffective Collision

18.1

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Collision TheoryCollision Theory•• The minimum energy that colliding particles The minimum energy that colliding particles

must have in order to react is called the must have in order to react is called the activation energyactivation energy ..

18.1Energy DiagramsEnergy Diagrams

Exothermic Endothermic

(a) Activation energy (Ea) for the forward reaction

(b) Activation energy (Ea) for the reverse reaction

(c) Delta H +200 kJ/mol+200 kJ/mol--100 kJ/mol100 kJ/mol

100 kJ/mol100 kJ/mol150 kJ/mol150 kJ/mol

300 kJ/mol300 kJ/mol50 kJ/mol50 kJ/mol


•• An An activated complexactivated complex is an unstable arrangement is an unstable arrangement of atoms that forms momentarily at the peak of the of atoms that forms momentarily at the peak of the activationactivation--energy barrier. energy barrier.

•• The activated complex is sometimes called the The activated complex is sometimes called the transition state.transition state.

18.1 Factors Affecting Reaction Factors Affecting Reaction RatesRates

�� The rate of a chemical reaction depends upon The rate of a chemical reaction depends upon temperature, concentration, particle size, and temperature, concentration, particle size, and the use of a catalyst.the use of a catalyst.

18.1

Factors Affecting Reaction Factors Affecting Reaction RatesRates

�� Animation 22 Animation 22 �� Explore several factors that control the speed Explore several factors that control the speed

of a reaction.of a reaction.


�� TemperatureTemperature•• Storing foods in a refrigerator keeps them fresh Storing foods in a refrigerator keeps them fresh

longer. Low temperatures slow microbial action.longer. Low temperatures slow microbial action.

18.1

8


�� ConcentrationConcentration

�� a. In air, a lighted splint glows and soon goes o ut. a. In air, a lighted splint glows and soon goes o ut. �� b. When placed in pure oxygen (higher oxygen b. When placed in pure oxygen (higher oxygen

concentration), the splint bursts into flame.concentration), the splint bursts into flame.


�� Particle SizeParticle Size

�� The minute size of the reactant particles (grain du st), The minute size of the reactant particles (grain du st), and the mixture of the grain dust with oxygen in th e and the mixture of the grain dust with oxygen in th e air caused the reaction to be explosive, destroying air caused the reaction to be explosive, destroying the grain elevator.the grain elevator.

18.1


�� CatalystsCatalysts


�� Simulation 23 Simulation 23 �� Explore the effects of concentration, Explore the effects of concentration,

temperature, and a catalyst on reaction rate.temperature, and a catalyst on reaction rate.


•• An An inhibitorinhibitor is a substance that interferes with the is a substance that interferes with the action of a catalyst. Antioxidants and antimicrobials action of a catalyst. Antioxidants and antimicrobials used in drying fruits and preserving fruit juices slow used in drying fruits and preserving fruit juices slow the action of microbes and limit contact with air.the action of microbes and limit contact with air.

18.1

18.1 Section Quiz.18.1 Section Quiz.

9


�� 1. The units below that would be appropriate 1. The units below that would be appropriate to measure the rate of a chemical reaction isto measure the rate of a chemical reaction is•• mmol/smmol/s..

•• mol/L.mol/L.

•• kJ/mol.kJ/mol.

•• h/mol.h/mol.


�� 2. In a chemical reaction, the energy of 2. In a chemical reaction, the energy of reactants is alwaysreactants is always•• greater than the energy of the products. greater than the energy of the products.

•• more than the activation energy.more than the activation energy.

•• less than the activation energy.less than the activation energy.

•• less than the energy of the products.less than the energy of the products.


�� 3. An increase in which one of the following 3. An increase in which one of the following will NOT increase the reaction rate?will NOT increase the reaction rate?•• temperaturetemperature

•• concentration of reactantsconcentration of reactants

•• total mass of reactantstotal mass of reactants

•• surface area of reactantssurface area of reactants

18.1 Section Quiz.18.1 Section Quiz.�� 4. A catalyst works because it 4. A catalyst works because it

•• lowers the activation energy.lowers the activation energy.

•• increases the temperature.increases the temperature.

•• is permanently changed in a reaction.is permanently changed in a reaction.

•• supplies energy to a reaction.supplies energy to a reaction.

Reversible ReactionsReversible Reactions

�� At chemical equilibrium, no net change occurs At chemical equilibrium, no net change occurs in the actual amounts of the components of in the actual amounts of the components of the system.the system.

18.2


•• A A reversible reactionreversible reaction is one in which the is one in which the conversion of reactants to products and the conversion of reactants to products and the conversion of products to reactants occur conversion of products to reactants occur simultaneously.simultaneously.

18.2

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Reversible ReactionsReversible Reactions18.2

At equilibrium, all three types of molecules are present.

SO2 and O2react to give

SO3

SO3decomposes to SO2 and O2


•• When the rates of the forward and reverse When the rates of the forward and reverse reactions are equal, the reaction has reached a reactions are equal, the reaction has reached a state of balance called state of balance called chemical equilibriumchemical equilibrium ..

•• The relative concentrations of the reactants and The relative concentrations of the reactants and products at equilibrium constitute the products at equilibrium constitute the equilibrium equilibrium positionposition of a reaction.of a reaction.

18.2

Reversible ReactionsReversible Reactions18.2 Factors Affecting Equilibrium: Factors Affecting Equilibrium:

Le Le ChChâtelierâtelier’’ss PrinciplePrinciple�� Stresses that upset the equilibrium of a Stresses that upset the equilibrium of a

chemical system include changes in the chemical system include changes in the concentration of reactants or productsconcentration of reactants or products, , changes in temperaturechanges in temperature, and , and changes in changes in pressurepressure..

�� Le Le ChâtelierChâtelier ’’ss principleprinciple : If a stress is applied : If a stress is applied to a system in dynamic equilibrium, the to a system in dynamic equilibrium, the system changes in a way that relieves the system changes in a way that relieves the stress.stress.

Factors Affecting Equilibrium: Factors Affecting Equilibrium: Le Le ChChâtelierâtelier’’ss PrinciplePrinciple

�� ConcentrationConcentration•• Rapid breathing during and after vigorous exercise Rapid breathing during and after vigorous exercise

helps reestablish the bodyhelps reestablish the body’’s correct COs correct CO22:H:H22COCO33

equilibrium, keeping the acid concentration in the equilibrium, keeping the acid concentration in the blood within a safe range.blood within a safe range.


�� Temperature Temperature •• DinitrogenDinitrogen tetroxide is a colorless gas; nitrogen tetroxide is a colorless gas; nitrogen

dioxide is a brown gas. The flask on the left is in a dioxide is a brown gas. The flask on the left is in a dish of hot water; the flask on the right is in ice.dish of hot water; the flask on the right is in ice.

18.2

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•• PressurePressure•• Pressure affects a mixture of nitrogen, hydrogen, Pressure affects a mixture of nitrogen, hydrogen,

and ammonia at equilibriumand ammonia at equilibrium

Conceptual Conceptual Problem 18.1Problem 18.1

Conceptual Problem 18.1Conceptual Problem 18.1Conceptual Conceptual

Problem 18.1Problem 18.1

18.2 Section Quiz.18.2 Section Quiz.18.2 Section Quiz.18.2 Section Quiz.

�� 1. In a reaction at equilibrium, reactants and 1. In a reaction at equilibrium, reactants and products products •• decrease in concentration.decrease in concentration.•• form at equal rates.form at equal rates.•• have equal concentrations.have equal concentrations.•• have stopped reacting.have stopped reacting.

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�� 2. In the reaction 2NO2. In the reaction 2NO22((gg) ) →→ 2NO(2NO(gg) + O) + O22((gg), ), increasing the pressure on the reaction would increasing the pressure on the reaction would cause cause •• the amount of NO to increase.the amount of NO to increase.

•• the amount of NOthe amount of NO22 to increase.to increase.

•• nothing to happen.nothing to happen.

•• the amount of Othe amount of O22 to increase.to increase.


�� 3. Changing which of the following would 3. Changing which of the following would NOT affect the equilibrium position of a NOT affect the equilibrium position of a chemical reaction?chemical reaction?•• concentration of a reactant onlyconcentration of a reactant only

•• concentration of a product onlyconcentration of a product only

•• temperature onlytemperature only

•• volume onlyvolume only

18.4

Entropy and Free EnergyEntropy and Free Energy�� Inside a pile of oily rags or a Inside a pile of oily rags or a

stack of hay that has not stack of hay that has not been thoroughly dried, been thoroughly dried, decomposition causes heat decomposition causes heat to build up. When heat to build up. When heat cannot escape, the cannot escape, the temperature can become temperature can become high enough to cause a fire. high enough to cause a fire. You will learn about the You will learn about the conditions that will produce conditions that will produce a spontaneous chemical a spontaneous chemical reaction.reaction.

Free Energy and SpontaneousFree Energy and SpontaneousReactionsReactions

•• A A spontaneous reactionspontaneous reaction occurs naturally and occurs naturally and favors the formation of products at the specified favors the formation of products at the specified conditions.conditions.

Free Energy and SpontaneousFree Energy and SpontaneousReactionsReactions

•• A A nonspontaneous reactionnonspontaneous reaction is a reaction that is a reaction that does not favor the formation of products at the does not favor the formation of products at the specified conditions.specified conditions.

Photosynthesis is a nonspontaneous reaction that requires an input of energy.

18.4Free Energy and SpontaneousFree Energy and SpontaneousReactionsReactions

•• Spontaneous reactions produce substantial Spontaneous reactions produce substantial amounts of products at equilibrium and release amounts of products at equilibrium and release free energy.free energy.

•• Free energyFree energy is energy that is available to do is energy that is available to do work.work.

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EntropyEntropy•• EntropyEntropy is a measure of the disorder of a system.is a measure of the disorder of a system.

�� Physical and chemical systems attain the lowest possible Physical and chemical systems attain the lowest possible energy.energy.

�� The The law of disorderlaw of disorder states that the natural tendency is for states that the natural tendency is for systems to move in the direction of maximum disorder or systems to move in the direction of maximum disorder or randomness. randomness.

18.4

EntropyEntropy

�� An increase in entropy favors the An increase in entropy favors the spontaneous chemical reaction; a decrease spontaneous chemical reaction; a decrease favors the nonspontaneous reaction.favors the nonspontaneous reaction.

18.4

EntropyEntropy

•• For a given substance, the entropy of the gas is For a given substance, the entropy of the gas is greater than the entropy of the liquid or the solid. greater than the entropy of the liquid or the solid. Similarly, the entropy of the liquid is greater than Similarly, the entropy of the liquid is greater than that of the solid.that of the solid.

18.4

EntropyEntropy•• Entropy increases when a substance is divided Entropy increases when a substance is divided

into parts.into parts.

EntropyEntropy•• Entropy tends to increase in chemical reactions in Entropy tends to increase in chemical reactions in

which the total number of product molecules is which the total number of product molecules is greater than the total number of reactant molecules.greater than the total number of reactant molecules.

18.4

EntropyEntropy

•• Entropy tends to increase when temperature Entropy tends to increase when temperature increases. As the temperature increases, the increases. As the temperature increases, the molecules move faster and faster, which molecules move faster and faster, which increases the disorder.increases the disorder.

18.4

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Enthalpy, Entropy, and Free Enthalpy, Entropy, and Free EnergyEnergy

�� The size and direction of enthalpy changes The size and direction of enthalpy changes and entropy changes together determine and entropy changes together determine whether a reaction is spontaneous; that is, whether a reaction is spontaneous; that is, whether it favors products and releases free whether it favors products and releases free energy.energy.

Enthalpy, Entropy, and Free Enthalpy, Entropy, and Free EnergyEnergy

Gibbs FreeGibbs Free--EnergyEnergy

�� Gibbs FreeGibbs Free--EnergyEnergy�� Is the Gibbs freeIs the Gibbs free--energy change positive or energy change positive or

negative in a spontaneous process?negative in a spontaneous process?

18.4 Gibbs FreeGibbs Free--EnergyEnergy

•• The The Gibbs freeGibbs free--energy changeenergy change is the maximum is the maximum amount of energy that can be coupled to another amount of energy that can be coupled to another process to do useful work.process to do useful work.

•• The numerical value of The numerical value of ∆∆GG is negative in spontaneous is negative in spontaneous processes because the system loses free energy.processes because the system loses free energy.

18.4

18.4 Section Quiz.18.4 Section Quiz.18.4 Section Quiz.18.4 Section Quiz.

�� 1. Free energy from a reaction is the amount 1. Free energy from a reaction is the amount of energy that is of energy that is •• absorbed by an entropy decrease.absorbed by an entropy decrease.•• equal to the enthalpy change.equal to the enthalpy change.•• wasted as heat.wasted as heat.•• available to do work.available to do work.

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�� 2. Free energy is always available from 2. Free energy is always available from reactions that are reactions that are •• endothermic. endothermic. •• nonspontaneousnonspontaneous..•• at equilibrium.at equilibrium.•• spontaneous.spontaneous.

18.4 Section Quiz.18.4 Section Quiz.�� 3. Choose the correct words for the spaces: 3. Choose the correct words for the spaces:

Spontaneous reactions produce ________ Spontaneous reactions produce ________ and substantial amounts of _________ at and substantial amounts of _________ at equilibrium.equilibrium.•• free energy, products free energy, products

•• no free energy, reactantsno free energy, reactants

•• free energy, reactantsfree energy, reactants

•• no free energy, productsno free energy, products


�� 4. Which of the following involves a decrease 4. Which of the following involves a decrease in entropy? in entropy? •• Natural gas burns.Natural gas burns.•• A liquid freezes.A liquid freezes.•• Dry ice sublimes.Dry ice sublimes.•• Water evaporates.Water evaporates.

18.4 Section Quiz.18.4 Section Quiz.�� 5. A reaction is spontaneous if 5. A reaction is spontaneous if

•• enthalpy decreases and entropy increases.enthalpy decreases and entropy increases.

•• enthalpy increases and entropy increases.enthalpy increases and entropy increases.

•• enthalpy decreases and entropy decreases.enthalpy decreases and entropy decreases.

•• enthalpy increases and entropy decreases.enthalpy increases and entropy decreases.

18.4 Section Quiz.18.4 Section Quiz.�� 6. Choose the correct words for the spaces: 6. Choose the correct words for the spaces:

Gibbs freeGibbs free--energy change is the _________ energy change is the _________ amount of energy that can be ___________ amount of energy that can be ___________ another process to do useful work.another process to do useful work.•• maximum, coupled tomaximum, coupled to

•• maximum, duplicated bymaximum, duplicated by

•• spontaneous, coupled tospontaneous, coupled to

•• minimum, duplicated byminimum, duplicated by

END OF SHOWEND OF SHOW

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CHAPTER 17: Heat vs. Temperature - pkwy.k12.mo.us · PDF fileCHAPTER 17: THERMOCHEMISTRY Page 504 – 539 Heat vs. Temperature ATOM ... Rates of Reaction The heat given off by the