thermochemistry

ThermochemistryThermochemistry

ObjectiveObjective• Introduction to ThermochemistryIntroduction to Thermochemistry

• Define TemperatureDefine Temperature

• Potential EnergyPotential Energy

• EnthalpyEnthalpy

• Endothermic and ExothermicEndothermic and Exothermic

• Entropy?Entropy?

Warm – up X2Warm – up X2

• What is potential Energy?What is potential Energy?

• Energy can not be created or Energy can not be created or destroyed!!destroyed!!

• Where does the energy come from Where does the energy come from when you burn gasoline?when you burn gasoline?

• How about an Explosion??How about an Explosion??

The Nobel Prize (Alfred Nobel)The Nobel Prize (Alfred Nobel)

• How Noble is the Nobel Prize??• Found that when you mixed Nitroglycerin

(shock sensitive) with diatomatious earth (inert) it was no longer nearly as shock sensitive.

• His fortune was made in Dynamite!

What happens after the What happens after the material explodes?material explodes?

• Is an explosion exothermic or Is an explosion exothermic or endothermic?endothermic?

• Is that positive or negative?Is that positive or negative?• Does the material contain more or Does the material contain more or

less potential energy after it less potential energy after it explodes?explodes?

• Loosing potential energy in the Loosing potential energy in the bondsbonds

What is an What is an Thermochemistry (V)??Thermochemistry (V)??

• The study of the transfer of of energy, The study of the transfer of of energy, as heat that is accompanied by as heat that is accompanied by chemical reactions and physical chemical reactions and physical changes.changes.

Thermochemical Equation (v)Thermochemical Equation (v)

•A Chemical equation that includes A Chemical equation that includes the enthalpy.the enthalpy.2H2H22(g) + O(g) + O22(g) (g) 2H 2H22O(g) + 483.6 kJO(g) + 483.6 kJ

The 483.6 kJ is the amount of energy released The 483.6 kJ is the amount of energy released (exothermic)(exothermic)

2H2H22O(g) + 483.6 kJ O(g) + 483.6 kJ 2H 2H22(g) + O(g) + O22(g)(g)

The 483.6 kJ is the amount of energy The 483.6 kJ is the amount of energy absorbed (endothermic)absorbed (endothermic)

Thermochemical EquationThermochemical EquationThe equations can also be written: The equations can also be written: 2H2H22(g) + O(g) + O22(g) (g) 2H 2H22O(g); O(g); ΔΔH= H= -- 483.6 kJ483.6 kJ

-483.6 kJ is negative (or exothermic) What 483.6 kJ is negative (or exothermic) What side?side?

-2H2H22O(g) O(g) 2H 2H22(g) + O(g) + O22(g); (g); ΔΔH= +H= +483.6 kJ483.6 kJ

483.6 kJ is positive (or endothermic)483.6 kJ is positive (or endothermic)

What side does it go on?What side does it go on?

Note the substances and moles formedNote the substances and moles formed

More Vocabulary for This ChapterMore Vocabulary for This Chapter

• Calorimeter – a device that is Calorimeter – a device that is intended to measure energy absorbed intended to measure energy absorbed or released.or released.

• Temperature – A measure of the Temperature – A measure of the average kinetic energy of the particles average kinetic energy of the particles in matter. (always Kelvin).in matter. (always Kelvin).

• Joule – The SI unit for energy. (N-m)Joule – The SI unit for energy. (N-m)

More Vocabulary for This ChapterMore Vocabulary for This Chapter

• Joule – The SI unit for energy.Joule – The SI unit for energy.

• So if I said Joule per gram: What does So if I said Joule per gram: What does that mean?that mean?

• If I said Joule per mole: What does If I said Joule per mole: What does that mean?that mean?

Enthalpy (ΔH) changeEnthalpy (ΔH) change

• Enthalpy has the symbol (H) and is the amount of energy contained within a system (bonds, state, temperature). Potential energy within the bonds lost or gained.

• Is it more or less stable after?

• If I set off some Trinitrotoluene (TNT) is it more or less stable after I set it off?

Vocabulary for This ChapterVocabulary for This Chapter•Enthalpy change – Amount of energy, as Enthalpy change – Amount of energy, as heat absorbed or released by a system at heat absorbed or released by a system at constant pressure.constant pressure.

ΔHΔHrxrx = H = Hproductsproducts – H – Hreactantsreactants

ΔHΔHmixingmixing = H = Hsolutionsolution – (H – (Hsolutesolute + H + Hsolventsolvent))

Note Enthalpy is an measure of potential Note Enthalpy is an measure of potential

energy or energy contained within the bonds.energy or energy contained within the bonds.

Enthalpy (ΔH) changeEnthalpy (ΔH) change

• Exothermic – release heat in a reaction!

• Endothermic absorb heat in a reaction!

• Exothermic ΔH is negative.

• Endothermic ΔH is positive.

Vocabulary for This ChapterVocabulary for This Chapter• Enthalpy change – Amount of energy, as Enthalpy change – Amount of energy, as

heat absorbed or released by a system at heat absorbed or released by a system at constant pressure.constant pressure.

• Enthalpy of reaction – is the quantity of Enthalpy of reaction – is the quantity of energy transferred as heat during a energy transferred as heat during a chemical reaction.chemical reaction.

• Endothermic – When heat is absorbed by Endothermic – When heat is absorbed by a system from the surroundings (+).a system from the surroundings (+).

• Exothermic – When heat is released by the Exothermic – When heat is released by the system to the surroundings (-)system to the surroundings (-)

The reason why exothermic is The reason why exothermic is neg and endothermic is neg and endothermic is

positive.positive.• It is adding or subtracting It is adding or subtracting

potential energy from the potential energy from the energy stored in the bonds.energy stored in the bonds.

Compounds whose enthalpies of Compounds whose enthalpies of formation are highly negativeformation are highly negative

a. Do not exist.a. Do not exist.

b. Are somewhat stable.b. Are somewhat stable.

c. Are very unstable.c. Are very unstable.

d. Are very stable.d. Are very stable.

Why???Why???

✔

Entropy Entropy S is a measure of disorderS is a measure of disorder • What is more random, has a higher entropy What is more random, has a higher entropy

ΔS ΔS ??? ???

Higher Entropy Higher Entropy ΔSΔS??????Type/more/lessType/more/less

http://www.baltimorediamonds.com/blog/wp-content/uploads/goincoins2.jpg

http://www.baltimorediamonds.com/blog/wp-content/uploads/goincoins2.jpg

EntropyEntropyMeasure of the degree of Measure of the degree of randomness in a system? (V)randomness in a system? (V)

S S 1.1. What is more random, What is more random, Solid, Liquid or Gas? Solid, Liquid or Gas?

Entropy S• Entropy is a measure of the disorder in a

system. If disorder increases the change in Entropy is positive.

• Change in Entropy is ΔS!

• If entropy increases disorder increases.

CO2 (s) CO2(g)

(ΔS positive or negative?)

Entropy SEntropy S• Entropy is a measure of the disorder in a system. Entropy is a measure of the disorder in a system.

If disorder increases the change in Entropy is If disorder increases the change in Entropy is positive.positive.

• Change in Entropy is ΔS!Change in Entropy is ΔS!

• If entropy increases disorder increases If entropy increases disorder increases

(In a Solution?)(In a Solution?)

NaCl(s) NaCl(s) Na Na++(aq) + Cl(aq) + Cl--(aq)(aq)

(ΔS positive or negative?)(ΔS positive or negative?)

Entropy Entropy SS What is more random What is more random Reactant or Product? Reactant or Product? 2H2H22(g) + O(g) + O22(g) (g) 2H 2H22O(O(ll))

S <0S <0

Two molecules of gas converting Two molecules of gas converting into one liquid.into one liquid.

Entropy Entropy SS

What is more random What is more random Reactant or Product? Reactant or Product?

3H3H22(g) + N(g) + N22(g) (g) 2NH 2NH33(g)(g)

S <0S <0Two molecules of gas converting Two molecules of gas converting

into one of gas.into one of gas.

Entropy Entropy SS What is more random What is more random Reactant or Product? Reactant or Product?

2C2C66HH66(l) + 15O(l) + 15O22(g) (g) 6H6H22O(g) + 12COO(g) + 12CO22(g)(g)

S > 0S > 0Two molecules of gas converting Two molecules of gas converting into one of gas.into one of gas.More or less favored? More!! More or less favored? More!!

Entropy Entropy SS What is more random What is more random Reactant or Product? Reactant or Product? KNOKNO33(s) (s) K K++(aq) + NO(aq) + NO33

--(aq)(aq)

S > 0S > 0Two molecules of solid converting Two molecules of solid converting into two moles of aqueous ions.into two moles of aqueous ions.More or less favored? More or less favored?

Entropy is also additiveEntropy is also additiveΔS = [Sum of SΔS = [Sum of Sproductsproducts – Sum of S – Sum of Sreactantsreactants]]

Problem:Problem:

AlAl22OO33(s) + 3H(s) + 3H22(g)(g)2Al(s) + 3H2Al(s) + 3H22O(g) O(g)

ΔS = ? If entropy ofΔS = ? If entropy of

AlAl22OO33(s) =51.00kJ/mol·K; Al(s) = 28.32 (s) =51.00kJ/mol·K; Al(s) = 28.32

kJ/mol·K; HkJ/mol·K; H22O(g) is 188.7 kJ/mol·K; O(g) is 188.7 kJ/mol·K;

HH22(g) is 130.6 kJ/mol·K .(g) is 130.6 kJ/mol·K .

Entropy S• Entropy is a measure of the disorder in a

system. If disorder increases the change in Entropy is positive.

• Change in Entropy is ΔS!

• If entropy increases disorder increases.

2NO(g) 2NO(g) N N22(g) + O(g) + O22(g) (g)

(ΔS positive or negative?)(ΔS positive or negative?)

Day 2 (Warm-up)Day 2 (Warm-up)

• Does Entropy increase or decrease?Does Entropy increase or decrease?

• Does Enthalpy increase or decrease?Does Enthalpy increase or decrease?

• Combustion of Liquid Octane (CCombustion of Liquid Octane (C88HH1818)?)?

• Evaporation of Water?Evaporation of Water?

The Most Expensive Combustion The Most Expensive Combustion Reaction!! Reaction!! (The Russians are coming!)(The Russians are coming!)

CCdiamonddiamond + O + O22 CO CO22 ΔH = -395.41 kJ/mol ΔH = -395.41 kJ/mol

Enthalpy (ΔH) change is theEnthalpy (ΔH) change is the

• a. pressure change of a system at constant temperature.

• b. entropy change of a system at constant pressure.

• c. temperature change of a system at constant pressure.

• d. amount of energy absorbed or lost by a system as energy is the form of heat.

ObjectiveObjective• Gibbs Free Energy (spontaneous Gibbs Free Energy (spontaneous

reactions)reactions)

• Introduction to Specific Heat Introduction to Specific Heat calculationscalculations

• Energy Curve, Activation EnergyEnergy Curve, Activation Energy

• Explain Hess’s Law Explain Hess’s Law

Spontaneous (v) reactionSpontaneous (v) reaction• A spontaneous process is the time-A spontaneous process is the time-

evolution of a system in which it releases evolution of a system in which it releases free energy (most often as heat) and moves (most often as heat) and moves to a lower, more thermodynamically to a lower, more thermodynamically stable, energy state. stable, energy state.

• Or the reaction happens…with no helpOr the reaction happens…with no help

• Free Energy????Free Energy????

• Thermodynamically stable???Thermodynamically stable???

• Ahhhhhhhh……………………..Ahhhhhhhh……………………..

http://en.wikipedia.org/wiki/Gibbs_free_energy

G = G = H - TH - TSSIf Negative SpontaneousIf Negative Spontaneous

• At 300 K is this reaction spontaneous, At 300 K is this reaction spontaneous, not spontaneous, or can it not be not spontaneous, or can it not be determined?determined?

CC22HH44 (g) + H (g) + H22(g) (g) C C22HH66(g)(g)

ΔH = -136.9kJ/mol; ΔS = -0.1207kJ/mol·K ΔH = -136.9kJ/mol; ΔS = -0.1207kJ/mol·K

G = G = H -TH -TS S

G =G = -136.9kJ/mol – (300K)(-0.121kJ/mol·K)-136.9kJ/mol – (300K)(-0.121kJ/mol·K)

-100.6 kJ/mol-100.6 kJ/mol

Gibbs Free Energy (ΔG)

• ΔG = Gibbs free EnergyΔG = Gibbs free Energy

• If negative the reaction is If negative the reaction is spontaneousspontaneous

• If positive will not happen.If positive will not happen.

ΔG = ΔH - TΔSΔG = ΔH - TΔS

The Driving Force In the Nature The Driving Force In the Nature of Reactionsof Reactions

Two factors effect whether a Two factors effect whether a reaction will occur reaction will occur spontaneously.spontaneously.

1.1. H – H – Enthalpy of formation if Enthalpy of formation if negative will favor negative will favor Spontaneous Spontaneous Reaction -- WHY??Reaction -- WHY??

The Driving Force In the Nature of The Driving Force In the Nature of ReactionsReactions

Factor Number TWO effect whether a Factor Number TWO effect whether a reaction will occur spontaneously.reaction will occur spontaneously.

G = G = H - TH - TS S 1.1. TTS – S – Entropy Term (Entropy Entropy Term (Entropy times temperature). If positive will times temperature). If positive will favor favor Spontaneous Reaction -- Spontaneous Reaction -- WHY??WHY??

Spontaneous reactions are driven bySpontaneous reactions are driven by

a. decreasing enthalpy and decreasing a. decreasing enthalpy and decreasing entropy.entropy.

b. decreasing enthalpy and increasing b. decreasing enthalpy and increasing entropy.entropy.

c. increasing enthalpy and decreasing c. increasing enthalpy and decreasing entropy.entropy.

d. increasing enthalpy and increasing d. increasing enthalpy and increasing entropy.entropy.

Vocabulary for This ChapterVocabulary for This Chapter•Enthalpy change – Amount of energy, as Enthalpy change – Amount of energy, as heat absorbed or released by a system at heat absorbed or released by a system at constant pressure.constant pressure.

•Enthalpy of reaction – is the quantity of Enthalpy of reaction – is the quantity of energy transferred as heat during a chemical energy transferred as heat during a chemical reaction.reaction.

ΔH = HΔH = Hproductsproducts – H – Hreactantsreactants

Note Enthalpy is an measure of potential Note Enthalpy is an measure of potential

energy or energy contained within the bonds.energy or energy contained within the bonds.

Thermochemical EquationThermochemical Equation

•A Chemical equation that includes A Chemical equation that includes the enthalpy.the enthalpy.2H2H22(g) + O(g) + O22(g) (g) 2H 2H22O(g) + 483.6 kJO(g) + 483.6 kJ

The 483.6 kJ is the amount of energy released The 483.6 kJ is the amount of energy released (exothermic)(exothermic)

2H2H22O(g) + 483.6 kJ O(g) + 483.6 kJ 2H 2H22(g) + O(g) + O22(g)(g)

The 483.6 kJ is the amount of energy The 483.6 kJ is the amount of energy absorbed (endothermic)absorbed (endothermic)

Thermochemical EquationThermochemical Equation

Write the Thermal Chemical Equation ForWrite the Thermal Chemical Equation For: : 2H2H22(g) + O(g) + O22(g) (g) 2H 2H22O(g); O(g); ΔΔH= H= -- 483.6 kJ483.6 kJ

-- 483.6 kJ is negative (or __________) 483.6 kJ is negative (or __________)

2H2H22O(g) O(g) 2H 2H22(g) + O(g) + O22(g); (g); ΔΔH= +H= +483.6 kJ483.6 kJ

483.6 kJ is positive (or ____________)483.6 kJ is positive (or ____________)

Note the substances and moles formedNote the substances and moles formed

Warm up Question

• Balance and write the thermochemical equation for the combustion of benzene (C6H6) ΔH = - 3476kJ/mol:

ObjectivesObjectives

• What is Activation Energy?What is Activation Energy?

• Why does it exist?Why does it exist?

• Potential Energy Diagram? Potential Energy Diagram?

• What is it and how to read it.What is it and how to read it.

Activation Energy• the minimum energy that must be the minimum energy that must be

put into a chemical system, put into a chemical system, containing potential for reactants to containing potential for reactants to react!react!

In order for the rock to In order for the rock to get to the bottom of the hill get to the bottom of the hill it has to go over the humpit has to go over the hump

In Chemical reactions, What causes the hump?

• Energy at which they collide (not all have the same energy). Why?? What surrounds an atom or molecule?

• Orientation (for most reactions to occur they have to have the correct orientation (meet the right way)

Collision Theory• When particles of the reactant hit each When particles of the reactant hit each

other, only a certain percentage of the other, only a certain percentage of the collisions cause a significant chemical collisions cause a significant chemical change.change.

Potential Energy Diagram

Which is exothermic and which is Which is exothermic and which is endothermic?.endothermic?.

Which curve shows more storage at the end?Which curve shows more storage at the end?

Catalyst (v)Catalyst (v)• A substance that is not used up in a A substance that is not used up in a

reaction that lowers the activation reaction that lowers the activation energy!!energy!!

Other Vocabulary for This ChapterOther Vocabulary for This Chapter

• Specific Heat – amount of energy Specific Heat – amount of energy required to raise the temperature of 1 required to raise the temperature of 1 gram, K (1 °C ).gram, K (1 °C ).

• Heat – Energy transferred between Heat – Energy transferred between matter due to their temperature matter due to their temperature differences. differences.

– Which way does heat flow.Which way does heat flow.

How much energy is absorbed as heat by 20. g of gold when it is heated from 25°C to 55°C? The specific heat of gold is 0.13 J/g·°C.

ProblemProblem

How much energy is needed to raise the How much energy is needed to raise the temperature of a 55g piece of aluminum temperature of a 55g piece of aluminum from 22.4from 22.4°C to 94.6 °C. °C to 94.6 °C.

Given: Specific Heat = Cp = 0.897J/g-Given: Specific Heat = Cp = 0.897J/g-K K

ProblemProblemGiven:Given:• An amount of water weighting 500 grams is in an An amount of water weighting 500 grams is in an

insulated container is being used to make tea. We insulated container is being used to make tea. We want to get the water from a temperature of 25°C want to get the water from a temperature of 25°C to 100°C. Assuming no boiling or vaporization to 100°C. Assuming no boiling or vaporization and no loss of heat to surroundings. How long will and no loss of heat to surroundings. How long will it take to heat this in a 1000 Watt microwave it take to heat this in a 1000 Watt microwave oven. oven.

• Specific heat of HSpecific heat of H22O = 4.18 J/g-K.O = 4.18 J/g-K.

• 1000 1000 wattwatt microwave oven supplies = 3,600,000 J/hr microwave oven supplies = 3,600,000 J/hr..

Calculate the time it takes to heat up the water.Calculate the time it takes to heat up the water.

How to manipulate How to manipulate thermochemical equationsthermochemical equations

2H2H22 + O + O22 2H 2H22OO ΔH = -483.6 kJΔH = -483.6 kJ

HH22 + + ½½OO22 H H22OO ΔH = -241.8 kJΔH = -241.8 kJ

4H4H22 + 2O + 2O22 4H 4H22OO ΔH = -967.2 kJΔH = -967.2 kJ

2H2H22O O 2H 2H22 + O + O22 ΔH = +483.6 kJΔH = +483.6 kJ


Want: C(s) + 2HWant: C(s) + 2H22(g) (g) CH CH44(g)(g) ΔH = ? kJΔH = ? kJ

Given:Given:

HH22(g) + (g) + ½½OO22(g) (g) H H22O(l)O(l) ΔH = -285.8 kJΔH = -285.8 kJ

C(s) + OC(s) + O22(g) (g) CO CO22(g)(g) ΔH = -393.5 kJΔH = -393.5 kJ

CHCH44 + 2O + 2O22 2H 2H22O + COO + CO22 ΔH = -890.8 kJΔH = -890.8 kJ

11stst Get reactants and products on the right Get reactants and products on the right sides of the equations:sides of the equations:

22ndnd Balance them Balance them33rdrd add them altogether add them altogether

The enthalpy of formation of an The enthalpy of formation of an element iselement is??

00Why???Why???Definition: The molar enthalpy of Definition: The molar enthalpy of formation Hformation Hf f is the enthalpy change is the enthalpy change that occurs when one mole of a that occurs when one mole of a compound is formed in their compound is formed in their standard state (1 atm, 25°C) standard state (1 atm, 25°C) (V)(V)



Given:Given:



CHCH44 + O + O22 2H 2H22O + COO + CO22 ΔH = -890.8 kJΔH = -890.8 kJ




a. do not exist.a. do not exist.

b. are somewhat stable.b. are somewhat stable.

c. are very unstable.c. are very unstable.

d. are very stable.d. are very stable.

Why???Why???

⏎

Dr. Canale, Why are you doing this to Dr. Canale, Why are you doing this to me are you trying to drive me insane???me are you trying to drive me insane???

YES I AM!!!!!!YES I AM!!!!!!

But also……..But also……..

Hess’s Law – The overall enthalpy Hess’s Law – The overall enthalpy change in a reaction is the sum of change in a reaction is the sum of enthalpy changes for the enthalpy changes for the individual steps in the process.individual steps in the process.

Very Important RulesVery Important Rules

• Enthalpy of Combustion Enthalpy of Combustion HHcc – The – The

enthalpy change that occurs during the enthalpy change that occurs during the

complete complete combustion of one mole of combustion of one mole of

reactantreactant..

CC66HH66 + + 77½½OO22 3H 3H22O + 6COO + 6CO22


• Enthalpy of Formation (heat of Enthalpy of Formation (heat of

formation) – The enthalpy change that formation) – The enthalpy change that

occurs during the formationoccurs during the formation of one of one

mole of product from it’s elementsmole of product from it’s elements..

6C + 6C + 22½½HH22 C C66HH55

6C + 3H6C + 3H22 C C66HH66

Problem

The enthalpy of formation of ethane C2H6 is: Write the equation!

ProblemProblem

The enthalpy of formation of Xylene The enthalpy of formation of Xylene CC88HH1010 is: Write the equation! is: Write the equation!

Hess’s Law – The overall enthalpy Hess’s Law – The overall enthalpy change in a reaction is the sum of change in a reaction is the sum of enthalpy changes for the individual steps enthalpy changes for the individual steps in the process.in the process.

ororA bond is a bond and as long as it’s the A bond is a bond and as long as it’s the same in the end no mater how it gets same in the end no mater how it gets there.there.



Given:Given:



CHCH44 + O + O22 2H 2H22O + COO + CO22 ΔH = -890.8 kJΔH = -890.8 kJ



The enthalpy of formation of an The enthalpy of formation of an element iselement is??

zerozero

Why???Why???



Given:Given:



CHCH44 + 2O + 2O22 2H 2H22O + COO + CO22 ΔH = -890.8 kJΔH = -890.8 kJ







reactantreactant..

CC66HH66 + + 77½½OO22 3H 3H22O + 6COO + 6CO22


• Enthalpy of Formation – The enthalpy Enthalpy of Formation – The enthalpy

change that occurs during the change that occurs during the Formation of Formation of

one mole of product from it’s elementsone mole of product from it’s elements..

6C + 6C + 22½½HH22 C C66HH55

6C + 3H6C + 3H22 C C66HH66






Why???Why???

Hess’s Law – The overall enthalpy Hess’s Law – The overall enthalpy change in a reaction is the sum of change in a reaction is the sum of enthalpy changes for the enthalpy changes for the individual steps in the process.individual steps in the process.

Graphite and diamond are different forms of Graphite and diamond are different forms of carbon, one just a little more valuable than carbon, one just a little more valuable than the other. Using these two equations, tell me the other. Using these two equations, tell me how much energy does it take to convert how much energy does it take to convert graphite to diamond?graphite to diamond?

CCgraphitegraphite C Cdiamonddiamond =? =?

CCgraphitegraphite + O + O22 CO CO22 ΔH = -393.5kJ ΔH = -393.5kJ

CCdiamonddiamond + O + O22 CO CO22 ΔH = -395.4kJ ΔH = -395.4kJ

Yes they burned a diamond!!!!!!Yes they burned a diamond!!!!!!

Carbon and Carbon monoxide can be Carbon and Carbon monoxide can be combusted in oxygen to form Carbon combusted in oxygen to form Carbon dioxide. Use Hess’s Law to compute the dioxide. Use Hess’s Law to compute the formation of carbon and oxygen to carbon formation of carbon and oxygen to carbon monoxide?monoxide?

CC + ½ O+ ½ O22 CO =? CO =?

C + OC + O22 CO CO22 ΔH = -393.5 kJ ΔH = -393.5 kJ

CO + ½ OCO + ½ O22 CO CO22 ΔH = -283.0 kJ ΔH = -283.0 kJ





reactantreactant..

CC66HH66 + + 77½½OO22 3H 3H22O + 6COO + 6CO22



change that occurs during the complete change that occurs during the complete

combustion of one mole of productcombustion of one mole of product..

6C + 6C + 22½½HH22 C C66HH55

6C + 3H6C + 3H22 C C66HH66






Why???Why???

((HHff) for 2N) for 2N22(g) + 5O(g) + 5O

22(g) (g) 2N 2N22OO55(g)(g)

HH22(g) + ½O(g) + ½O22(g) (g) H H22O (l)O (l)

H = -285.8 kJH = -285.8 kJ

NN22OO55(g) + H(g) + H22O(l)O(l) 2HNO 2HNO33(l)(l)

H = -76.6kJH = -76.6kJ

1/2N1/2N22(g) +3/2O(g) +3/2O22(g) + 1/2H(g) + 1/2H22(g) (g) HNO HNO33(l)(l)

H = -174.1kJH = -174.1kJ

Do you Remember Free Energy?Do you Remember Free Energy?

• You know Gibbs Free Energy??You know Gibbs Free Energy??

• ΔG = ΔG =

• The reaction happens if….The reaction happens if….

• ΔG = - (negative)ΔG = - (negative)

ΔG = ΔH - TΔSΔG = ΔH - TΔS

H – Enthalpy of formation if negative H – Enthalpy of formation if negative will favor will favor Spontaneous Reaction -- Spontaneous Reaction --

WHY??WHY??

Because Because H is negative and when it H is negative and when it is negative it has less potential is negative it has less potential energy and is more stable.energy and is more stable.

What is more stable a rock at a What is more stable a rock at a steeper angle or a rock at a slight steeper angle or a rock at a slight angle???angle???

If the reaction is spontaneous the If the reaction is spontaneous the H of H of reaction will probably be negative reaction will probably be negative

What is more stable, products or reactants?What is more stable, products or reactants?

Two moles of HTwo moles of H22 and one mole of O and one mole of O22 or two or two

moles of Hmoles of H2200

2H2H22(g)(g) + O+ O22(g) (g) 2H 2H220(g)0(g)

HH220 and the reaction actually has 0 and the reaction actually has

negative enthalpy or exothermic, negative enthalpy or exothermic,

and is spontaneous. (and is spontaneous. (H = -571.6 kJ)H = -571.6 kJ)



Two moles of Iron and 3 moles of OTwo moles of Iron and 3 moles of O22 or two or two

moles of Femoles of Fe22003 3 (Red Iron Oxide = RUST)(Red Iron Oxide = RUST)

4Fe(s)4Fe(s) + 3O+ 3O22(g) (g) 2Fe 2Fe220033(s)(s)

FeFe220033 and the reaction actually has and the reaction actually has


and is spontaneous. and is spontaneous.

What is the What is the H of reaction? H of reaction?

4Fe(s)4Fe(s) + 3O+ 3O22(g) (g) 2Fe 2Fe220033(s) (s) H = ?H = ?

Formed from it’s elements??Formed from it’s elements??

HHff = −825.50 kJ = −825.50 kJ

Definition of Definition of HHff ?? ??

H for reaction isH for reaction is - 1651.0 kJ - 1651.0 kJ------- -------



Two moles of Butane and 13 moles of OTwo moles of Butane and 13 moles of O22 or or

10 moles of Water and 8 moles of CO10 moles of Water and 8 moles of CO22??

2C2C44HH1010 + 13O + 13O22 10H 10H220 + 8CO0 + 8CO22

HH220 and CO0 and CO22 and the reaction and the reaction

actually has negative enthalpy or actually has negative enthalpy or

exothermic, and is spontaneous. exothermic, and is spontaneous.




reactantreactant..

CC66HH66 + + 77½½OO22 3H 3H22O + 6COO + 6CO22


change that occurs during the complete change that occurs during the complete

combustion of one mole of product.combustion of one mole of product.

6C + 6C + 22½½HH22 C C66HH55

((HHff) for 2N) for 2N22(g) + 5O(g) + 5O

22(g) (g) 2N 2N22OO55(g)(g)

HH22(g) + ½O(g) + ½O22(g) (g) H H22O (l)O (l)

H = -285.8 kJH = -285.8 kJ

NN22OO55(g) + H(g) + H22O(l)O(l) 2HNO 2HNO33(l)(l)

H = -76.6kJH = -76.6kJ

1/2N1/2N22(g) +3/2O(g) +3/2O22(g) + 1/2H(g) + 1/2H22(g) (g) HNO HNO33(l)(l)

H = -174.1kJH = -174.1kJ





2H2H22(g)(g) + O+ O22(g) (g) 2H 2H220(g)0(g)




What is the What is the H of reaction? H of reaction?

4Fe(s)4Fe(s) + 3O+ 3O22(g) (g) 2Fe 2Fe220033(s) (s) H = ?H = ?

Formed from it’s elements??Formed from it’s elements??

HHff = −825.50 kJ = −825.50 kJ

Definition of Definition of HHff ?? ??

H for reaction isH for reaction is - 1651.0 kJ - 1651.0 kJ------- -------

H – Enthalpy of formation if negative H – Enthalpy of formation if negative will favor will favor Spontaneous Reaction -- Spontaneous Reaction --

WHY??WHY??

Because Because H is negative and when it H is negative and when it is negative it has less potential is negative it has less potential energy and is more stable.energy and is more stable.

What is more stable a rock at a What is more stable a rock at a steeper angle or a rock at a slight steeper angle or a rock at a slight angle???angle???





2H2H22(g)(g) + O+ O22(g) (g) 2H 2H220(g)0(g)




Thermite I (red)Thermite I (red)

FeFe22OO33 + 2Al + 2Al Al Al22OO33 + 2Fe; + 2Fe; ΔH = ?ΔH = ?

2Fe + 1½O2Fe + 1½O22 Fe Fe22OO33; ΔH = -826 kJ; ΔH = -826 kJ

2Al + 1½O2Al + 1½O22AlAl22OO33; ΔH = -1676 kJ; ΔH = -1676 kJ

FeFe22OO33 + 2Al + 2Al Al Al22OO33 + 2Fe; + 2Fe; ΔH= -850kJΔH= -850kJ

ΔH= -425kJ/mol Fe; ΔH=-850kJ/mol AlΔH= -425kJ/mol Fe; ΔH=-850kJ/mol Al22OO33

Thermite II (Black)Thermite II (Black)

3Fe3Fe33OO44(s) + 8Al(s)(s) + 8Al(s)4Al4Al22OO33(s)+9Fe(s); (s)+9Fe(s); ΔH = ?ΔH = ?

3Fe + 2O3Fe + 2O22 Fe Fe33OO44; ΔH = -1117 kJ; ΔH = -1117 kJ

2Al + 1½O2Al + 1½O22AlAl22OO33; ΔH = -1676 kJ; ΔH = -1676 kJ

FeFe33OO44 3Fe + 2O 3Fe + 2O22; ΔH = +1117 kJ; ΔH = +1117 kJ



3Fe + 2O3Fe + 2O22 Fe Fe33OO44; ΔH = -1117 kJ; ΔH = -1117 kJ

(4){2Al + 1½O(4){2Al + 1½O22AlAl22OO33; ΔH = -1676 kJ}; ΔH = -1676 kJ}

(3){Fe(3){Fe33OO44 3Fe + 2O 3Fe + 2O22; ΔH = +1117 kJ}; ΔH = +1117 kJ}



8Al + 6O8Al + 6O224Al4Al22OO33; ΔH = -6704 kJ}; ΔH = -6704 kJ}

3Fe3Fe33OO44 9Fe + 6O 9Fe + 6O22; ΔH = +3351 kJ}; ΔH = +3351 kJ}



8Al(s) + 6O8Al(s) + 6O22(g)(g)4Al4Al22OO33(s); ΔH = -6704 kJ}(s); ΔH = -6704 kJ}

3Fe3Fe33OO44(s)(s) 9Fe(s) + 6O 9Fe(s) + 6O22(g); ΔH = +3351 kJ}(g); ΔH = +3351 kJ}________________________________________________________________________________________________________________________________________________________________________________________

3Fe3Fe33OO44(s)+8Al(s)(s)+8Al(s)4Al4Al22OO33(s)+9Fe(s);(s)+9Fe(s);ΔHΔH -3353 kJ -3353 kJ

-373 kJ/mole Fe; 838.3kJ/mol Al-373 kJ/mole Fe; 838.3kJ/mol Al22OO33

thermochemistry

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