05 energy and thermo(1)

7/29/2019 05 Energy and Thermo(1)

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Biochemistry 5

FUNDAMENTALS

Reaction Rates and Equilibrium

AUSOM


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Important concepts


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Energy and ThermodynamicsKinetic Energy

TemperatureF, C, K

F -> C TF = 1.80(Tc) + 32

C -> F Tc = (TF - 32)/1.80

C -> K TK = Tc + 273


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BioChemical Reactions


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Consider A B

[A]

[B]


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Potential Energy

Loss of Energy, Exothermic

Gain of Energy, Endothermic


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Biological Energy is the Gibbs Free Energy G

Heat can be measured by Calorimetry


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Spontaneous


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Combined 1st & 2nd LawsG = H - TS


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Example

Which would you expect to have higher entropy?

Water Ice

Water Steam20 individual AA a polypeptide containing 20 AA

Solid NaCl NaCl (aq)

Boltzmann S = k ln ( )

= Number of States


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Biological Energy is the Gibbs Free Energy G

A -> B


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Types of reactionsConsider if y-axis is Heat


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Consider [A] -> [B]

!

G = 0@ equilibrium

!!


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@ equilibrium

!!

!Changing the concentrations will move the reaction

Le Chateliers


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Keq is a constant


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[O2]

%Hb

bound


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COUPLED REACTIONS

Chemical Analogy

Mechanical Analogy


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COUPLED REACTIONS IN GLYCOLYSIS

ADP + Pi -> ATP G +


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ATP, ~ 7Kcal/mol

ADP, ~ 7Kcal/mol

AMP, ~ 2Kcal/mol


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Oxidative Phosphorylation


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Summary


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Spontaneous and Nonspontaneous Changes. Spontaneousprocesses take place naturally with no apparent cause or stimulus.Process spontaneity depends on the energy and entropy changesthat accompany the process. Energy decreases and entropyincreases favor spontaneity. However, a nonspontaneous change inone of these factors can be compensated for by a large

spontaneous change in the other to cause processes to bespontaneous.

Reaction Rates. The speed of a reaction is called a reaction rate,and can be determined by measuring how fast reactants are usedup or products are formed.

Molecular Collisions. Explanations of how reactions take place arecalled reaction mechanisms. most mechanisms are based on threeassumptions: (1) molecules must collide with each other, (2) thecollision must involve a certain minimum of energy, and (3) somecolliding molecules must be oriented in a specific way duringcollision in order to react.


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Energy Diagrams. Energy relationships for reactions can be representedby energy diagrams in which energy is plotted versus the reaction progress.The concepts of exergonic and endergonic reactions and activation energyare clearly represented by such diagrams.

Factors That Influence Reaction Rates. Four factors affect the rates of allreactions: (1) the nature of the reactants, (2) reactant concentrations, (3)reactant temperature, and (4) the presence of catalysts.

Chemical Equilibrium. Reactions are in equilibrium when the rate of theforward reaction is equal to the rate of the reverse reaction. Equilibrium isemphasized in reactions by writing double arrows pointing in both directionsbetween reactants and products.

Position of Equilibrium. The relative amounts of reactants and productspresent in a system at equilibrium defines the position of equilibrium. Theequilibrium position is toward the right when a large amount of product ispresent, and toward the left when a large amount of reactant is present. Theposition is indicated by the value of the equilibrium constant.


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Factors That Influence EquilibriumPosition. Factors known to influence the

position of equilibrium include changes in

amount of reactants and/or products, andchanges in temperature. The influence of

such factors can be predicted by using Le

Chatelier's principle. Catalysts cannotchange the position of equilibrium.


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Formative Assessment


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A nitrogen gas sample is compressedto the point of liquification. This change

is state is accompanied by which of the

following changes.Entropy and energy decrease

Entropy and energy increase

Entropy increases but energy decreasesEnergy increases but entropy decreases


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Entropy and energy decrease


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The rate of a chemical reaction must beexpressed in minutes.

True

False


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False


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For the reactiondepicted in Figure

One, (b) refers to:

time of flightheat of formation

activated complex

activation energy

heat of sublimationFigure one


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activation energy


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The reaction depicted in Figure One isexothermic

True

False


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True


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For a homogeneous catalysis:The reactants must reach the surface

An enzyme is involved

One must raise the activation energyThe catalyst must be in the same state as

the reactants


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The catalyst must be in the same stateas the reactants


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For a system in equilibrium:the rate of the forward and reverse

reactions are the same

the concentrations of the reactants andproducts are the same

the solution is saturated

the solvent must be water


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the rate of the forward and reversereactions are the same


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For the following system in equilibrium:2NO2 (g) N2O4 (g),

what effect will increasing pressure

have?shift to the left

shift to the right

no effectreduce the 2NO2 concentration


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shift to the right


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For a reaction to be spontaneous,which if the following must be true.

delta H must be negative

delta H must be positivedelta S must be negative

delta S must be positive

delta G must be negativedelta G must be positive


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delta G must be negative


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The end

05 energy and thermo(1)

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