chemical equilibrium chapter 16 n.
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CHEMICAL EQUILIBRIUM Chapter 16 - PowerPoint PPT Presentation


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CHEMICAL EQUILIBRIUM Chapter 16. “Systems”: two reactions that differ only in direction. Any reversible reaction. H 2 + I 2 ↔ 2HI. noted by the double arrow; ↔. TWO REACTIONS. only difference is the Direction. H 2 + I 2 ↔ 2HI. reactants. products. 2HI ↔ H 2 + I 2. Left. Right.

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systems two reactions that differ only in direction
“Systems”: two reactions that differ only in direction
  • Any reversible reaction

H2 + I2↔ 2HI

noted by the double arrow; ↔

two reactions
TWO REACTIONS
  • only difference is the Direction

H2 + I2↔ 2HI

reactants

products

2HI ↔ H2 + I2

Left

Right

reversible reactions
Reversible Reactions

H2 + I2 ↔ 2HI

  • the products may react back to original reactants.
  • “closed system”:

ONLY if all reactant are present

  • If one piece is completely gone it has ”gone to competition” and no longer reversible
examples reversible reactions
Examples: Reversible Reactions.
  • Unopened Soda
  • Breathing
  • Rechargeable batteries
  • Color changing shirt
equilibrium
Equilibrium
  • The state in which a chemical reaction and its reverse reaction occur at the same rate.
properties of an equilibrium
Properties of an Equilibrium

Equilibrium systems are

  • DYNAMIC (in constant motion)
  • REVERSIBLE
  • can be approached from either direction

Pink to blue

Co(H2O)6Cl2 ---> Co(H2O)4Cl2 + 2 H2O

Blue to pink

Co(H2O)4Cl2+ 2 H2O ---> Co(H2O)6Cl2

equilibrium1
Equilibrium

Rates = 0

No change in the amounts

reversible reactions1

Equilibrium achieved

Reversible Reactions

Product conc. increases and then becomes constant at equilibrium

Reactant conc. declines and then becomes constant at equilibrium

chemical equilibrium
Chemical Equilibrium

Fe3+ + SCN-aFeSCN2+

At Equilibrium: RATES ARE EQUAL

  • the concentrations of reactants and products are constant.

D [ ]’s = 0

  • The forward and reverse reactions continue after equilibrium is attained.
reaction quotient
Reaction Quotient

At anypointin the reaction

H2 + I2 --->2 HI

the reacton quotient q
The Reacton Quotient, Q

In general, all reacting chemical systems are characterized by their REACTION QUOTIENT, Q.

When the system is at equilibrium, Q = K

the equilibrium constant
THE EQUILIBRIUM CONSTANT

For any type of chemical equilibrium of the type

aA + bB--->cC + dD

the following is a CONSTANT (at a given T)

If K is known, then we can predict concs. of products or reactants.

writing and manipulating k expressions
Writing and Manipulating K Expressions

Solids NEVER appear in equilibrium expressions.

S(s) + O2(g) ---> SO2(g)

writing and manipulating k expressions1
Writing and Manipulating K Expressions

Liquids NEVER appear in equilibrium expressions.

NH3(aq) + H2O(liq) ---> NH4+(aq) + OH-(aq)

product or reactant favored
Product- or Reactant Favored

Product-favored

Reactant-favored

slide21
For: N2(g) + 3 H2(g) ---> 2 NH3(g)

Using K: Is the reaction product-favored or reactant-favored?

When K is much greater than 1

the reaction is strongly

product-favored.

slide22
For

AgCl(s) g Ag+(aq) + Cl-(aq)

Kc = [Ag+] [Cl-] = 1.8 x 10-5

If K is much less than 1

The reaction is strongly reactant-favored.

Ag+(aq) + Cl-(aq) gAgCl(s)

is product-favored.

using k
Using K:

Can determine if the reaction is at equilibrium.

slide24
If [iso] = 0.35 M and [n] = 0.15 M, are you at equilibrium?

If not, which way does the reaction “shift” to approach equilibrium?

slide25
REACTION QUOTIENT, Q

Characterize all chemical systems

If Q = K, then system is at equilibrium.

Q (2.33) < K (2.5)

Reaction is NOT at equilibrium,

[iso] must ________ and [n] must ____________.

experimental determination of equilibrium constant k
Experimental Determination of Equilibrium Constant, K

2 NOCl(g) --->2 NO(g) + Cl2(g)

Place 2.00 mol of NOCl is a 1.00 L flask. At equilibrium you find 0.66 mol/L of NO.

Calculate K.

Set of an “ICE” table of concentrations

[NOCl] [NO] [Cl2]

Initial 2.00 0 0

Change

Equilibrium 0.66

determining k
Determining K

2 NOCl(g) ---> 2 NO(g) + Cl2(g)

[NOCl] [NO] [Cl2]

Initial 2.00 0 0

Change -0.66 +0.66 +0.33

Equilibrium 1.34 0.66 0.33

slide28
2 NOCl(g) ---> 2 NO(g) + Cl2(g)

[NOCl] [NO] [Cl2]

Initial 2.00 0 0

Change -0.66 +0.66 +0.33

Equilibrium 1.34 0.66 0.33