1.approachequil.ppt

7/24/2019 1.approachequil.ppt

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ApproachingEquilibrium

Lesson 1


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Approaching Equilibrium

Many chemical reactions are reversibleif the activation

energy is low.

Reactants Products


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energy is low.

Reactants Products

Always on left Always on right


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energy is low.

Reactants Products


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energy is low.

Reactants Products

Forward Rate is from

left to right


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Reactants Products


Forward Rate

Reverse Rate


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Reactants Products


Reverse Rate

Forward Rate


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Reactants Products


Reverse Rate

Forward Rate


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Reactants Products


Reverse Rate

Forward Rate


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Reactants Products


Reverse Rate

Forward Rate


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Reactants Products


Reverse Rate

Forward Rate

Are Equal


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Reactants Products


Reverse Rate

Forward Rate

Are Equal

Are onstant


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Reactants Products

Reverse Rate

Forward Rate

Are Equal

Are onstant

!ame as before


from Products


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"ime #Reactant$ Forward Rate #Product$ Reverse Rate %etRate

0 8000 170 0 0 170

5 7500 160 1000 16 144

10 6800 145 2000 20 125

15 5600 120 2500 30 90

20 4600 100 3200 40 60

25 3600 84 4000 50 34

30 2900 75 4900 56 19

35 2000 65 6000 58 7

40 1600 60 6000 60 0

45 1600 60 6000 60 0

50 1600 60 6000 60 0


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Equilibrium has been attained after 40 minutes. The forwardand

reverse ratesare equaland the reactantand productconcentrations

are constant.

G h h [ ] d [ d ] ilib i i h d


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Graph the [reactant]and [product]as equilibrium is approached.

Concentration

8000

7000

6000

5000

4000

3000

2000

1000

0 15 30 Time

equilibrium

G h h f d & ilib i i


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Graph the forward, reverse, & net ratesas equilibrium is

approached.

Rate

160

140

120

100

80

60

40

20

0 15 30 Time

equilibrium

A hi E ilib i


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Reactant concentrationsstart high and decreaseas the reaction

proceeds. The forward rate, which depends on collisions of thereactants, also decreases.

Product concentrationsstart at zero and increaseas the reaction

proceeds. The reverse rate, which depends on collisions of the products,also increases.

Eventually the forward rateis equal to the reverse rateand the

concentrationsare constant.This is equilibrium.

Ch t i ti f S t t E ilib i


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Characteristics of a System at Equilibrium

The Forward rate= The Reverse rate

The Reactant and Product concentrationsare constant

The Macroscopic(observable) propertiesare constant

The system is Dynamicas the forward and reverse reactions continue.

The equilibriumcan be approachedfrom starting with reactantsor

starting with products.


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Reactants Products


from Products

Reverse Rate

Forward Rate


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Reactants Products

Reverse Rate

Forward Rate


from Products


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Reactants Products

Reverse Rate

Forward Rate


from Products


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Reactants Products

Reverse Rate

Forward Rate


from Products


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Reactants Products

Reverse Rate

Forward Rate


from Products


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Reactants Products

Reverse Rate

Forward Rate

Are Equal

Are onstant

!ame as before


from Products

If you start with products all aspects of the approach to equilibrium are


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If you startwith productsall aspects of the approach to equilibrium are

reversed!

Productsand Reverse Ratedecrease

Reactantsand Forward Rateincreases

Conditions Necessary for Equilibrium


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Conditions Necessary for Equilibrium

The system is closed.

The temperature is constant.

The Eais lowenough so that the reaction is reversible.

Simulation1
http://web.umr.edu/~gbert/LGH/hepler.htmlhttp://web.umr.edu/~gbert/LGH/hepler.html

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