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# C. Law of Chemical Equilibrium - PowerPoint PPT Presentation

Equilibrium website. C. Law of Chemical Equilibrium. 50. 45. 40. 35. 30. Reactants. moles. 25. 20. Products. 15. 10. 40. 40. 5. 35. 35. 0. 30. 30. A. B. C. D. 25. 25. Reactants. moles. 20. Reactants. 20. moles. Products. Products. 15. 15. 10. 10. 5. 5. 0.

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C. Law of Chemical Equilibrium

50

45

40

35

30

Reactants

moles

25

20

Products

15

10

40

40

5

35

35

0

30

30

A

B

C

D

25

25

Reactants

moles

20

Reactants

20

moles

Products

Products

15

15

10

10

5

5

0

0

A

B

C

D

A

B

C

D

At equilibrium, [reactants] and [products] are constant.

Ratio of [products]:[reactants] will not change, even if concentrations change

If we double the amount of A, the reaction shifts to maintain the same ratio of products to reactants

Number which indicates ratio of the [prod] to [react]

[products]

Keq =

[reactants]

[reactants]

Keq =

2. Meaning of Keq

If we have more reactants than products at equilibrium,

5 M

Keq is small

= 0.5

10 M

A Keq < 1 means more reactants

Reverse reaction is favored

If we have more products than reactants at equilibrium,

100 M

Keq is big

= 10

10 M

A Keq >1 means more products

Forward reaction is favored

Example - For 2 H2O <==> H3O+ + OH-, Keq = 1 x 10-14. Which is higher [H2O] or [OH-] ?

Keq is less than 1, so more reactants

[H2O] is higher

A. Ag(NH3)2+ <==> Ag+ + 2 NH3

B. N2 + 3 H2 <==> 2 NH3

Keq = 8.9 x 10-8

Less than 1

Reverse reaction

Keq = 6.7 x 105

More than 1

Forward reaction

Changing Keq values

Pressure and concentrations will not change the ratio of [products] :[reactants]

If you add more reactants or products to one side, the equilibrium will shift to maintain the same ratio.

The only way to alter the value of a chemical

reaction's Keq is to change the temperature!

Ksp reaction.

Solubililty Product Constant

Chemical (s) Chemical (aq)

Everytime a solid chemical is dissolved in water, the equation can be written the same way.

When we write the Keq value for this, we end up with

Chemical (aq)

Chemical (s)

Keq =

This type of Keq is called Ksp – Solubility product constant

Meaning of Ksp

High Ksp

Lots of chemical has dissolved in water

soluble

Low Ksp

Little of chemical has dissolved in water

insoluble

No chemical has a Ksp of zero. Nothing is completely insoluble.

a. AgBr or ZnCO3?

b. CaSO4 or PbI2?