Chapter 19 “Reaction Rates and Equilibrium”. Section 19.1 Rates of Reaction OBJECTIVES...

Chapter 19Chapter 19“Reaction Rates and Equilibrium”“Reaction Rates and Equilibrium”

Section 19.1 Rates of ReactionSection 19.1 Rates of Reaction

OBJECTIVESOBJECTIVESDescribeDescribe how to express the how to express the

rate of a chemical reaction.rate of a chemical reaction.

Section 19.1 Rates of ReactionSection 19.1 Rates of Reaction

OBJECTIVESOBJECTIVESIdentifyIdentify four factors that four factors that

influence the rate of a influence the rate of a chemical reaction.chemical reaction.

Collision TheoryCollision Theory Reactions can occur:Reactions can occur:

Very fast – such as a firecrackerVery fast – such as a firecracker Very slow – such as the time it took for Very slow – such as the time it took for

dead plants to make coaldead plants to make coal A “rate” is a measure of the speed of A “rate” is a measure of the speed of

any change that occurs within an any change that occurs within an interval of timeinterval of time

In chemistry, reaction rate is expressed In chemistry, reaction rate is expressed as the amount of as the amount of reactant changing per reactant changing per unit timeunit time

Collision ModelCollision Model•Key Idea: Molecules must collide to react.

•However, only a small fraction of collisions produces a reaction. Why?

•Particles lacking the necessary kinetic energy to react bounce apart unchanged when they collide

Collision ModelCollision Model• Collisions must have enough energy Collisions must have enough energy

to produce the reaction (must equal to produce the reaction (must equal or exceed the or exceed the activation energyactivation energy – – the minimum energy needed to the minimum energy needed to react).react).

• Think of clay clumps thrown Think of clay clumps thrown together gently – they don’t stick, together gently – they don’t stick, but if thrown together forcefully, they but if thrown together forcefully, they stick tightly to each other.stick tightly to each other.

Collision ModelCollision Model An “activated complex” is an unstable An “activated complex” is an unstable

arrangement of atoms that forms arrangement of atoms that forms momentarily (typically about 10momentarily (typically about 10-13-13 seconds) at the peak of the activation-seconds) at the peak of the activation-energy barrier.energy barrier. This is sometimes called the transition This is sometimes called the transition

statestate Results in either a) forming products, or Results in either a) forming products, or

b) reformation of reactantsb) reformation of reactants Both outcomes are equally likelyBoth outcomes are equally likely

Collision ModelCollision Model The collision theory explains why The collision theory explains why

some naturally occurring reactions some naturally occurring reactions are very sloware very slow Carbon and oxygen react when Carbon and oxygen react when

charcoal burns, but this has a very charcoal burns, but this has a very high activation energyhigh activation energy

At room temperature, the collisions At room temperature, the collisions between carbon and oxygen are not between carbon and oxygen are not enough to cause a reactionenough to cause a reaction

Factors Affecting RateFactors Affecting Rate1) Temperature

Increasing temperature always increases the rate of a reaction.

2) Surface AreaIncreasing surface area increases the rate of a reaction

3) ConcentrationIncreasing concentration USUALLY

increases the rate of a reaction4) Presence of Catalysts

CatalystsCatalystsCatalystCatalyst: A substance that speeds : A substance that speeds up a reaction, without being up a reaction, without being consumed itself in the reactionconsumed itself in the reactionEnzymeEnzyme: A large molecule (usually : A large molecule (usually a protein) that catalyzes biological a protein) that catalyzes biological reactions.reactions.

Human body temperature = 37 Human body temperature = 37 ooC, much C, much too low for digestion reactions without too low for digestion reactions without catalysts.catalysts.

InhibitorsInhibitors – interfere with the action of a – interfere with the action of a catalyst; reactions slow or even stopcatalyst; reactions slow or even stop

Endothermic Reaction withEndothermic Reaction witha Catalysta Catalyst

Exothermic Reaction with a Exothermic Reaction with a CatalystCatalyst

Section 19.2 Reversible Section 19.2 Reversible Reactions and EquilibriumReactions and Equilibrium

OBJECTIVESOBJECTIVESDescribeDescribe how the amounts of how the amounts of

reactants and products reactants and products change in a chemical system change in a chemical system at equilibrium.at equilibrium.


OBJECTIVESOBJECTIVESIdentifyIdentify three stresses that three stresses that

can change the equilibrium can change the equilibrium position of a chemical position of a chemical system.system.


OBJECTIVESOBJECTIVESExplainExplain what the value of K what the value of Keqeq

indicates about the position indicates about the position of equilibrium.of equilibrium.

Reversible ReactionsReversible Reactions Some reactions do not go to Some reactions do not go to

completion as we have assumedcompletion as we have assumed They may be They may be reversiblereversible – a reaction – a reaction

in which the conversion of reactants to in which the conversion of reactants to products and the conversion of products and the conversion of products to reactants occur products to reactants occur simultaneouslysimultaneously

Forward: 2SOForward: 2SO2(g)2(g) + O + O2(g)2(g) →→ 2SO 2SO3(g)3(g)

Reverse: Reverse: 2SO2SO2(g)2(g) + O + O2(g)2(g) ←← 2SO 2SO3(g)3(g)

Reversible ReactionsReversible Reactions The two equations can be combined The two equations can be combined

into one, by using a into one, by using a double arrowdouble arrow, , which tells us that it is a reversible which tells us that it is a reversible reaction:reaction:

2SO2SO2(g)2(g) + O + O2(g)2(g) ↔ 2SO↔ 2SO3(g)3(g)

A chemical equilibrium occurs, and A chemical equilibrium occurs, and no net changeno net change occurs in the actual occurs in the actual amounts of the components of the amounts of the components of the system.system.

Reversible ReactionsReversible Reactions Even though the Even though the ratesrates of the forward of the forward

and reverse are equal, the and reverse are equal, the concentrationsconcentrations of components on both of components on both sides may not be equalsides may not be equal An equlibrium position may be shown:An equlibrium position may be shown:

A A B B oror A BA B1% 99% 99% 1%1% 99% 99% 1% It depends on which side is favored; almost It depends on which side is favored; almost

all reactions are reversible to some extentall reactions are reversible to some extent

Equilibrium ConstantsEquilibrium Constants

• Chemists generally express the Chemists generally express the position of equilibrium in terms of position of equilibrium in terms of numerical valuesnumerical valuesThese values relate to the These values relate to the

amountsamounts of reactants and of reactants and products at equilibriumproducts at equilibrium

This is called the equilibrium This is called the equilibrium constant, and abbreviated Kconstant, and abbreviated Keqeq

Equilibrium ConstantsEquilibrium Constants

• consider this reaction:consider this reaction: aA + bB aA + bB cC + dD cC + dD The equilibrium constant (KThe equilibrium constant (Keqeq) is the ) is the

ratioratio of product concentration to the of product concentration to the reactant concentration at equilibrium, reactant concentration at equilibrium, with each concentration raised to a with each concentration raised to a power (= the balancing coefficient)power (= the balancing coefficient)

Equilibrium ConstantsEquilibrium Constants• consider this reaction:consider this reaction:

aA + bB aA + bB cC + dD cC + dD Thus, the Thus, the ““mass actionmass action expression”expression”

has the general form:has the general form:

[C][C]cc x [D] x [D]dd

[A][A]aa x [B] x [B]bb

(brackets: [ ] = molarity concentration)(brackets: [ ] = molarity concentration)

KKeqeq ==

Equilibrium ConstantsEquilibrium Constants• the equilibrium constants provide the equilibrium constants provide

valuable information, such as valuable information, such as whether whether productsproducts or or reactantsreactants are are favored:favored: KKeqeq > 1, products favored at equilibrium > 1, products favored at equilibrium

KKeq eq < 1, reactants favored at equilibrium< 1, reactants favored at equilibrium

Le Chatelier’s PrincipleLe Chatelier’s Principle The French chemist Henri Le The French chemist Henri Le

Chatelier (1850-1936) studied how Chatelier (1850-1936) studied how the equilibrium position the equilibrium position shiftsshifts as a as a result of changing conditionsresult of changing conditions

Le Chatelier’s principle: Le Chatelier’s principle: If stress is If stress is applied to a system at equilibrium, applied to a system at equilibrium, the system changes in a way that the system changes in a way that relieves the stressrelieves the stress

Le Chatelier’s PrincipleLe Chatelier’s Principle What items did he consider to be What items did he consider to be

stressstress on the equilibrium: on the equilibrium:1)1) ConcentrationConcentration2)2) TemperatureTemperature3)3) PressurePressure

• ConcentrationConcentration – adding more – adding more reactant produces more product, reactant produces more product, and removing the product as it and removing the product as it forms will produce more productforms will produce more product

Each of these will now be discussed in detail

Le Chatelier’s PrincipleLe Chatelier’s Principle• TemperatureTemperature – increasing the – increasing the

temperature causes the equilibrium temperature causes the equilibrium position to shift in the direction that position to shift in the direction that absorbs heatabsorbs heat• If heat is one of the products (just like a If heat is one of the products (just like a

chemical), it is part of the equilibriumchemical), it is part of the equilibrium• so cooling an exothermic reaction will so cooling an exothermic reaction will

produce more product, and heating it would produce more product, and heating it would shift the reaction to the reactant side of the shift the reaction to the reactant side of the equilibriumequilibrium

Le Chatelier’s PrincipleLe Chatelier’s Principle• PressurePressure – changes in pressure will only – changes in pressure will only

effect gaseous equilibriaeffect gaseous equilibria• Increasing the pressure will usually favor Increasing the pressure will usually favor

the direction that has fewer moleculesthe direction that has fewer molecules

NN2(g)2(g) + 3H + 3H2(g)2(g) → 2NH→ 2NH3(g)3(g)

• For every two molecules of ammonia For every two molecules of ammonia made, four molecules of reactant are made, four molecules of reactant are used up – the equilibrium used up – the equilibrium shifts to the shifts to the rightright with an increase in pressure with an increase in pressure

Common Ion EffectCommon Ion Effect A A “common ion”“common ion” is an ion that is found in is an ion that is found in

both salts in a solutionboth salts in a solution exampleexample: You have a solution of : You have a solution of leadlead

(II) chromate. You now add some (II) chromate. You now add some leadlead (II) nitrate to the solution. (II) nitrate to the solution.The The lead (II)lead (II) is a common ion is a common ion

This causes a shift in equilibrium (due This causes a shift in equilibrium (due to Le Chatelier’s principle regarding to Le Chatelier’s principle regarding concentration), and is called the concentration), and is called the common ion effectcommon ion effect

Section 19.3Section 19.3Solubility EquilibriumSolubility Equilibrium

OBJECTIVESOBJECTIVESDescribeDescribe the relationship the relationship

between the solubility product between the solubility product constant and the solubility of a constant and the solubility of a compound.compound.

Solubility Product ConstantSolubility Product Constant Ionic compounds (salts) differ in Ionic compounds (salts) differ in

their solubilitiestheir solubilities All “insoluble” salts will actually All “insoluble” salts will actually

dissolve to dissolve to somesome extent in water extent in waterBetter said to be Better said to be slightlyslightly, or , or

sparinglysparingly, soluble in water, soluble in water

Solubility Product ConstantSolubility Product Constant

Consider: AgClConsider: AgCl(s)(s) Ag Ag++(aq)(aq) + Cl + Cl--(aq)(aq)

The The “equilibrium expression”“equilibrium expression” is: is:

[ Ag[ Ag+ + ] x [ Cl] x [ Cl- - ]]

[ AgCl ][ AgCl ] Keq =

What was the physical state of the AgCl?

Solubility Product ConstantSolubility Product Constant AgCl existed as a solid material, and AgCl existed as a solid material, and

was not in dissolved in solutionwas not in dissolved in solution the [ AgCl ] is the [ AgCl ] is constantconstant as long as some as long as some

undissolved solid is presentundissolved solid is present By multiplying the two constants, a new By multiplying the two constants, a new

constant is developed, and is called the constant is developed, and is called the “solubility product constant”“solubility product constant” (K (Kspsp):):

[AgCl] =[AgCl] = [Ag1+] x [Cl1-] = Ksp

Solubility Product ConstantSolubility Product Constant Values of solubility product constants Values of solubility product constants

are given for some common slightly are given for some common slightly soluble salts (text pg. 632) soluble salts (text pg. 632)

KKspsp = [Ag = [Ag1+1+] x [Cl] x [Cl1-1-]]

KKspsp = 1.8 x 10 = 1.8 x 10-10-10

The smaller the numerical value of KThe smaller the numerical value of Kspsp, the , the

lower the solubility of the compoundlower the solubility of the compound AgCl is usually considered “insoluble” AgCl is usually considered “insoluble”

because of its low valuebecause of its low value

Solubility Product ConstantSolubility Product Constant

To solve problems:To solve problems: a) write the balanced equation, which splits a) write the balanced equation, which splits

the chemical into its ionsthe chemical into its ions

b) write the “equilibrium expression”, and b) write the “equilibrium expression”, and

c) fill in the values known; calculate answerc) fill in the values known; calculate answer

Section 19.4Section 19.4Entropy and Free EnergyEntropy and Free Energy

OBJECTIVESOBJECTIVESIdentifyIdentify two characteristics of two characteristics of

spontaneous reactions.spontaneous reactions.


OBJECTIVESOBJECTIVESDescribeDescribe the role of entropy the role of entropy

in chemical reactions.in chemical reactions.


OBJECTIVESOBJECTIVESIdentifyIdentify two factors that two factors that

determine the spontaneity of determine the spontaneity of a reaction.a reaction.


OBJECTIVESOBJECTIVESDefineDefine Gibbs free-energy Gibbs free-energy

change.change.

Free Energy andFree Energy andSpontaneous ReactionsSpontaneous Reactions

Many chemical and physical processes Many chemical and physical processes release energy, and that can be used to release energy, and that can be used to bring about other changesbring about other changes The energy in a chemical reaction can be The energy in a chemical reaction can be

harnessed to do work, such as moving the harnessed to do work, such as moving the pistons in your car’s enginepistons in your car’s engine

Free energyFree energy is energy that is available is energy that is available to do workto do work ……but that does not mean it will be used but that does not mean it will be used

efficientlyefficiently


Your car’s engine is only about 30 % Your car’s engine is only about 30 % efficient, and this is used to propel itefficient, and this is used to propel it The remaining 70 % is lost as friction The remaining 70 % is lost as friction

and waste heatand waste heat No process can be made 100 % No process can be made 100 %

efficientefficient Even living things, which are among Even living things, which are among

the most efficient users of free energy, the most efficient users of free energy, are seldom more than 70 % efficientare seldom more than 70 % efficient


We can only get energy from a We can only get energy from a reaction that actually occurs, not reaction that actually occurs, not just theoretically:just theoretically: COCO2(g)2(g) → C→ C(s)(s) + O + O2(g)2(g) this is a balanced equation, and is the this is a balanced equation, and is the

reverse of combustionreverse of combustion Experience tells us this does not tend Experience tells us this does not tend

to occur, but instead happens in the to occur, but instead happens in the reverse directionreverse direction


The world of balanced chemical The world of balanced chemical equations is divided into two equations is divided into two groups:groups:

1)1) Equations representing reactions Equations representing reactions that actually occurthat actually occur

2)2) Equations representing reactions Equations representing reactions that do not tend to occur (or at least that do not tend to occur (or at least not efficiently)not efficiently)


The first, (those that actually occur) and The first, (those that actually occur) and more important group involves more important group involves processes that are spontaneousprocesses that are spontaneous A A spontaneous reactionspontaneous reaction occurs naturally, occurs naturally,

and favors the formation of products at the and favors the formation of products at the specified conditionsspecified conditions

They produce substantial amounts of They produce substantial amounts of product at equilibrium, and release free product at equilibrium, and release free energyenergy

Example: a fireworks display – page 567 Example: a fireworks display – page 567


In contrast, a In contrast, a nonspontaneous reactionnonspontaneous reaction is a reaction that does not favor the is a reaction that does not favor the formation of products at the specified formation of products at the specified conditionsconditions These do not give substantial amounts of These do not give substantial amounts of

product at equilibriumproduct at equilibrium Think of soda pop bubbling the COThink of soda pop bubbling the CO22 out: out:

this is spontaneous, whereas the COthis is spontaneous, whereas the CO22 going back into solution happens very going back into solution happens very little, and is nonspontaneouslittle, and is nonspontaneous

Spontaneous ReactionsSpontaneous Reactions Do not confuse the words Do not confuse the words spontaneousspontaneous and and

instantaneousinstantaneous. Spontaneous just simply . Spontaneous just simply means that it will work by itself, but does not means that it will work by itself, but does not say anything about how fast the reaction will say anything about how fast the reaction will take place – it may take 20 years to react, take place – it may take 20 years to react, but it will eventually react.but it will eventually react. Some spontaneous reactions are very slow:Some spontaneous reactions are very slow:

sugar + oxygen sugar + oxygen →→ carbon dioxide and water, but a bowl of carbon dioxide and water, but a bowl of sugar sugar appearsappears to be doing nothing (it is reacting, but to be doing nothing (it is reacting, but would take thousands of years)would take thousands of years)

At room temperature, it is very slow; apply heat and the At room temperature, it is very slow; apply heat and the reaction is fast; thus changing the conditions (temp. or reaction is fast; thus changing the conditions (temp. or pressure) may determine whether or not it is spontaneouspressure) may determine whether or not it is spontaneous

EntropyEntropy EntropyEntropy is a measure of disorder, and is is a measure of disorder, and is

usually measured in units of usually measured in units of J/molJ/mol.KK; ; there are no negative values of entropythere are no negative values of entropy

The The law of disorderlaw of disorder states the natural states the natural tendency is for systems to move to the tendency is for systems to move to the direction of maximum disorderdirection of maximum disorder Your room NEVER cleans itself (disorder to Your room NEVER cleans itself (disorder to

order?)order?) An increase in entropy (+ value) favors An increase in entropy (+ value) favors

the spontaneous chemical reactionthe spontaneous chemical reaction A decrease in entropy (- value) favors the A decrease in entropy (- value) favors the

nonspontaneous reactionnonspontaneous reaction

Enthalpy and EntropyEnthalpy and Entropy

1)Reactions tend to proceed in the direction that lowers the energy of the system (H, enthalpy).

2)Reactions tend to proceed in the direction that increases the disorder of the system (S, entropy).

and,

Enthalpy and EntropyEnthalpy and Entropy These are the two “drivers” to every These are the two “drivers” to every

equation.equation. If they both AGREE the reaction should be If they both AGREE the reaction should be

spontaneous, IT WILL be spontaneous at all spontaneous, IT WILL be spontaneous at all temperatures, and you will not be able to stop temperatures, and you will not be able to stop the reaction without separating the reactantsthe reaction without separating the reactants

If they both AGREE that the reaction should If they both AGREE that the reaction should NOT be spontaneous, it will NOT work at NOT be spontaneous, it will NOT work at ANY temperature, no matter how much you ANY temperature, no matter how much you heat it, add pressure, or anything else!heat it, add pressure, or anything else!

Enthalpy and EntropyEnthalpy and Entropy The size and direction of enthalpy and The size and direction of enthalpy and

entropy changes entropy changes togethertogether determine determine whether a reaction is spontaneouswhether a reaction is spontaneous

If the two drivers disagree on whether or If the two drivers disagree on whether or not it should be spontaneous, a third party not it should be spontaneous, a third party ((Gibb’s free energyGibb’s free energy) is called in to act as ) is called in to act as the “judge” about what temperatures it will the “judge” about what temperatures it will be spontaneous, and what the temp. is.be spontaneous, and what the temp. is. But, it WILL work and be spontaneous at But, it WILL work and be spontaneous at

some temperature!some temperature!

Spontaneity of ReactionsSpontaneity of ReactionsReactions proceed spontaneously in the direction that lowers their Gibb’s free energy, G.

G = H - TS (T is Kelvin temp.)

If G is negative, the reaction is spontaneous. (system loses free energy)

If G is positive, the reaction is NOT spontaneous. (requires work be expended)

Spontaneity of ReactionsSpontaneity of Reactions Therefore, if the enthalpy and entropy Therefore, if the enthalpy and entropy

do not agree with each other as to what do not agree with each other as to what should happen:should happen: Gibbs free-energy says that they are both Gibbs free-energy says that they are both

correct, the reaction will occurcorrect, the reaction will occur But the Gibbs free-energy will decide the But the Gibbs free-energy will decide the

conditions of temperature that it will conditions of temperature that it will happenhappen

When When G = 0, the reaction will reverse G = 0, the reaction will reverse direction (it is now at equilibrium)direction (it is now at equilibrium)

Section 19.5 The ProgressSection 19.5 The Progressof Chemical Reactionsof Chemical Reactions

OBJECTIVESOBJECTIVESDescribeDescribe the general the general

relationship between the relationship between the value of the specific rate value of the specific rate constant, constant, kk, and the speed of , and the speed of a chemical reaction.a chemical reaction.

Section 19.5 The ProgressSection 19.5 The Progressof Chemical Reactionsof Chemical Reactions

OBJECTIVESOBJECTIVESInterpretInterpret the hills and valleys the hills and valleys

in a reaction progress curve.in a reaction progress curve.

Rate LawsRate Laws For the equation: A For the equation: A → B, the rate at → B, the rate at

which A forms B can be expressed as which A forms B can be expressed as the change in A (or the change in A (or ΔΔA) with time, A) with time, where the beginning concentration Awhere the beginning concentration A11

is at time tis at time t11, and concentration A, and concentration A22 is at is at

a later time ta later time t22

ΔΔA A concentration Aconcentration A22 – concentration A – concentration A11

ΔΔt tt t22 – t – t11

Rate = - = -

Rate LawsRate Laws Since A is decreasing, its Since A is decreasing, its

concentration is smaller at a later concentration is smaller at a later time than initially, so time than initially, so ΔΔA is negativeA is negative The negative sign is needed to make The negative sign is needed to make

the rate positive, as all rates must be.the rate positive, as all rates must be. The rate of disappearance of A is The rate of disappearance of A is

proportional to concentration of A: proportional to concentration of A: ΔΔAA

ΔΔtt- α [A]

Rate LawsRate Laws

ΔΔAA

ΔΔtt

• This equation, called a This equation, called a rate lawrate law, is , is an expression for the rate of a an expression for the rate of a reaction in terms of the reaction in terms of the concentration of reactants.concentration of reactants.

= k x [A]Rate = -

Rate LawsRate Laws The The specific rate constantspecific rate constant ( (kk) for a ) for a

reaction is a proportionality constant reaction is a proportionality constant relating the concentrations of reactants relating the concentrations of reactants to the rate of reactionto the rate of reactionThe value of the specific rate The value of the specific rate

constant, constant, kk, is , is large if the products large if the products form quicklyform quickly

The value of The value of kk is is small if the products small if the products form slowlyform slowly

Rate LawsRate Laws The “The “order of a reactionorder of a reaction” is the ” is the power power

to which the concentration of a to which the concentration of a reactant must be raisedreactant must be raised to give the to give the experimentally observed relationship experimentally observed relationship between concentration and ratebetween concentration and rate

For the equation: aA + bB For the equation: aA + bB → cC + dD,→ cC + dD,

Rate = Rate = kk[A][A]aa[B][B]bb

Rate LawsRate Laws Rate = Rate = kk[A][A]aa[B][B]bb

Notice that the rate law which governs Notice that the rate law which governs the speed of a reaction is based on the speed of a reaction is based on THREE things:THREE things:

1)1) The concentration (molarity) of each of the The concentration (molarity) of each of the reactantsreactants

2)2) The power to which each of these reactants The power to which each of these reactants is raisedis raised

3)3) The value of The value of kk or the rate constant (which is or the rate constant (which is different for every different equation.)different for every different equation.)

Rate LawsRate Laws Rate = Rate = kk[A][A]aa[B][B]bb

The powers to which the concentrations are The powers to which the concentrations are raised are calculated from experimental data, raised are calculated from experimental data, and the rate constant is also calculated. and the rate constant is also calculated. These powers are called These powers are called ORDERSORDERS..

For example, if the exponent of A was 2, we For example, if the exponent of A was 2, we would say the reaction is 2would say the reaction is 2ndnd order in A; if the order in A; if the exponent of B was 3, we would say the exponent of B was 3, we would say the reaction is 3reaction is 3rdrd order in B. order in B.

The overall reaction order is the The overall reaction order is the SUMSUM of all the of all the orders of reactants. If the order of A was 2, orders of reactants. If the order of A was 2, and B was 3, the overall reaction order is 5.and B was 3, the overall reaction order is 5.

Reaction MechanismsReaction Mechanisms

An elementary reaction is a reaction in An elementary reaction is a reaction in which the reactants are converted to which the reactants are converted to products in a products in a single stepsingle step

Only has one activation-energy peak Only has one activation-energy peak between reactants and productsbetween reactants and products

Peaks are energies of activated Peaks are energies of activated complexes, and valleys are the energy of complexes, and valleys are the energy of an intermediatean intermediate

Reaction MechanismsReaction Mechanisms An intermediate is a product of one An intermediate is a product of one

of the steps in the reaction of the steps in the reaction mechanismmechanism Remember how Hess’s law of Remember how Hess’s law of

summation was the total of individual summation was the total of individual reactions added together to give one reactions added together to give one equation?equation?

- Page 578

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Chapter 19 “Reaction Rates and Equilibrium”. Section 19.1 Rates of Reaction OBJECTIVES...

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