Approaching Equilibrium Lesson 1. Approaching Equilibrium Many chemical reactions are reversible if...

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Approaching Equilibrium Lesson 1

Transcript of Approaching Equilibrium Lesson 1. Approaching Equilibrium Many chemical reactions are reversible if...

ApproachingEquilibrium

Lesson 1

Approaching Equilibrium Many chemical reactions are reversible if the activation energy is low. 

Reactants ⇌ Products 

Approaching Equilibrium Many chemical reactions are reversible if the activation energy is low. 

Reactants ⇌ ProductsAlways on left Always on right 

 

Approaching Equilibrium Many chemical reactions are reversible if the activation energy is low. 

Reactants ⇌ Products

 

Approaching Equilibrium Many chemical reactions are reversible if the activation energy is low. 

Reactants ⇌ Products

 

Forward Rate is fromleft to right

 

Approaching Equilibrium Many chemical reactions are reversible if the activation energy is low. 

Reactants ⇌ Products 

Reverse Rate is from right to left  

Lets see what happens to some reactants if they are placed in a reaction vessel and allowed to react.  

Reactants Products

Approaching Equilibrium

Forward Rate

Reverse Rate

Reactants Products

Approaching Equilibrium

Reverse Rate

Forward Rate

Reactants Products

Approaching Equilibrium

Reverse Rate

Forward Rate

Reactants Products

Approaching Equilibrium

Reverse Rate

Forward Rate

Reactants Products

Approaching Equilibrium

Reverse Rate

Forward Rate

Reactants Products

Approaching Equilibrium

Reverse Rate

Forward Rate

Reactants Products

Approaching Equilibrium

Reverse Rate

Forward Rate

Reactants Products

Approaching Equilibrium

Reverse Rate

Forward Rate

Are Equal

Reactants Products

Approaching Equilibrium

Reverse Rate

Forward Rate

Are Equal

Are Constant

Reactants Products

Reverse Rate

Forward Rate

Are Equal

Are ConstantSame as before

Approaching Equilibriumfrom Products

Time [Reactant] Forward Rate [Product] Reverse Rate Net Rate 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

Equilibrium has been attained after 40 minutes. The forward and reverse rates are equal and the reactant and product concentrations are constant.

 

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

 Concentration  8000 

7000    6000

5000

  4000 

3000

2000

1000

0 15 30 Time

equilibrium

 

Graph the forward, reverse, & net rates as equilibrium is approached.

 Rate  160 

140    120

100

  80 

60

40

20

0 15 30 Time

equilibrium

Approaching Equilibrium

Reactant concentrations start high and decrease as the reaction proceeds. The forward rate, which depends on collisions of the reactants, also decreases.  Product concentrations start at zero and increase as the reaction proceeds. The reverse rate, which depends on collisions of the products, also increases.  Eventually the forward rate is equal to the reverse rate and the concentrations are constant. This is equilibrium.

Characteristics of a System at Equilibrium  The Forward rate = The Reverse rate  The Reactant and Product concentrations are constant The Macroscopic (observable) properties are constant The system is Dynamic as the forward and reverse reactions continue. The equilibrium can be approached from starting with reactants or starting with products.

Reactants Products

Approaching Equilibriumfrom Products

Reverse Rate

Forward Rate

Reactants Products

Reverse Rate

Forward Rate

Approaching Equilibriumfrom Products

Reactants Products

Reverse Rate

Forward Rate

Approaching Equilibriumfrom Products

Reactants Products

Reverse Rate

Forward Rate

Approaching Equilibriumfrom Products

Reactants Products

Reverse Rate

Forward Rate

Approaching Equilibriumfrom Products

Reactants Products

Reverse Rate

Forward Rate

Are Equal

Are ConstantSame as before

Approaching Equilibriumfrom Products

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

Products and Reverse Rate decrease

Reactants and Forward Rate increases

Conditions Necessary for Equilibrium The system is closed.  The temperature is constant. The Ea is low enough so that the reaction is reversible.

Simulation1