CHEM 102 Chapter Notes - Chapter 16: Reaction Quotient, Dynamic Equilibrium, Equilibrium Constant

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9 Mar 2016

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Dynamic equilibrium for a chemical reaction is the condition in which the rate of the forward reaction equals the rate of the reverse reaction. Physical or chemical processes in dynamic equilibrium; Explain the statement, equilibrium does not depend on direction of approach ; K > 1 reverse reaction is favored; forward reaction does not proceed very far. K 1 neither direction is favored; forward reaction proceeds about halfway. K < 1 forward reaction is favored; forward reaction proceeds essentially to completion. Calculation of equilibrium constants for related reactions. So far, we have expressed the equilibrium constant only in terms of the concentrations of the reactants and products. For gaseous reactions, the partial pressure of a particular gas is proportional to its concentration. therefore, we can also express the equilibrium constant in terms of the partial pressures of the reactants and products. To gauge the progress of a reaction relative to equilibrium, we use a quantity called the reaction quotient.

Related Questions

1) Express the equilibrium constant for the following reaction?

2) For the reaction of carbon with carbon dioxide to make carbon monoxide, the reaction is as follows.

Write the equilibrium constant expression for the K_c?

3) Which of the following statements is FALSE?

a) When K is very large, the forward reaction is favored and essentially goes to completion.

b) None of the answers are correct.

c) If K is very large it implies that the reaction is very fast at producing products.

d) When K is very small, the reverse reaction is favored and the forward reaction does not proceed to a great extent.

4)The equilibrium constant for the production of carbon dioxide from carbon monoxide and oxygen is 2 x 10¹¹.

This means that the reaction mixture at equilibrium is likely to consist of

a) mostly starting materials.

b) twice as much starting material as a product.

c) mostly products.

d) twice as much product as starting material.

grayant910

To understand the relationship between the equilibrium constant and rate constants.

For a general chemical equation

A+BâC+D

the equilibrium constant can be expressed as a ratio of the concentrations:

Kc=[C][D][A][B]

If this is an elementary chemical reaction, then there is a single forward rate and a single reverse rate for this reaction, which can be written as follows:

forward ratereverse rate==kf[A][B]kr[C][D]

where kf and kr are the forward and reverse rate constants, respectively. When equilibrium is reached, the forward and reverse rates are equal:

kf[A][B]=kr[C][D]

Thus, the rate constants are related to the equilibrium constant in the following manner:

Kc=kfkr=[C][D][A][B]

Part A

For a certain reaction, Kc = 5.79Ã10⁸ and kf= 634 Mâ2â sâ1 . Calculate the value of the reverse rate constant, kr, given that the reverse reaction is of the same molecularity as the forward reaction.

Express your answer with the appropriate units. Include explicit multiplication within units, for example to enter Mâ2â sâ1include â (multiplication dot) between each measurement.

kr =

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Part B

For a different reaction, Kc = 7.92Ã10⁵, kf=6.77Ã105sâ1, and kr= 0.855 sâ1 . Adding a catalyst increases the forward rate constant to 2.24Ã10⁸ sâ1 . What is the new value of the reverse reaction constant, kr, after adding catalyst?

Express your answer with the appropriate units. Include explicit multiplication within units, for example to enter Mâ2â sâ1include â (multiplication dot) between each measurement.

kr =

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Part C

Yet another reaction has an equilibrium constant Kc=4.32Ã105 at 25 âC. It is an exothermic reaction, giving off quite a bit of heat while the reaction proceeds. If the temperature is raised to 200 âC , what will happen to the equilibrium constant?

The equilibrium constant will

Yet another reaction has an equilibrium constant at 25 . It is an exothermic reaction, giving off quite a bit of heat while the reaction proceeds. If the temperature is raised to 200 , what will happen to the equilibrium constant?

increase.

decrease.

not change.

1) If the temperature of an endothermic reaction at equilibriumcould be increased instantaneously, what would be the instantaneouseffect on Q and K before equilibrium was againachieved?

a.	Q would increase and K would stay thesame.
b.	Q would decrease and K would stay thesame.
c.	Q would stay the same and K wouldincrease.
d.	Q would stay the same and K woulddecrease.
e.	Both Q and K would stay the same.

2) Which of the following is true regarding the effect of acatalyst on chemical equilibrium?

a.	Only the forward rate increases so the quantity of productsincreases.
b.	Only the forward rate increases but the quantity of productsremains the same.
c.	Both the forward and reverse rates increase and the quantity ofproducts increases.
d.	Both the forward and reverse rates increase but the quantity ofproducts is unchanged.
e.	The effect varies depending on whether the reaction isendothermic or exothermic.

3) The equilibrium constant for a given reaction __________

a.	does not change with temperature.
b.	always increases with temperature.
c.	always decreases with temperature.
d.	increases with temperature for exothermic reactions only.
e.	increases with temperature for endothermic reactions only,

Fill in the blanks

1) Chemical equilibrium arises from the __________ of chemicalreactions and is defined when the __________ of the forwardreaction is equal to the __________ of the reverse reaction.

2) Students often write expressions for the equilibrium constantK_c and reaction quotient Q_cin exactly the same way. To avoid confusion, you must rememberthatK_c uses concentrations under __________conditions while Q_c uses concentrations under__________ conditions.

3) If Q for a reaction is greater than K, thereaction will be __________. If Q for a reaction is lessthan K, the reaction will be __________. If Q fora reaction is equal to K, the reaction will be__________.

4) How and why are the expressions for homogeneous equilibriumconstants different from the expressions for heterogeneousequilibrium constants?

CHEM 102 Chapter Notes - Chapter 16: Reaction Quotient, Dynamic Equilibrium, Equilibrium Constant

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