Chemical Equilibrium: A Foundation for Chemistry, Slides of Analytical Chemistry

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: Chemical Equilibrium

• Should be review from General Chemistry
• Foundation of the Rest of the Course!

The Difference Between Equilibrium and Kinetics?

Differences between Equilibrium

and Kinetics?

• (^) Kinetics
• (^) How fast does a

reaction take?

• (^) Equilibrium
• (^) Will it happen?

Energy

Reaction

NO!

reactant

product

Energy

Reaction

reactant

product

E a

H

In general

aA + bB cC + dD

K = [C]

c [D]

d

---

[A]

a [B]

b

= constant if at equilibrium

WHAT?

• If a reaction is not at equilibrium, due to an

outside stress, the reaction will “shift” to

relieve the stress.

HENRI LOUIS LE CHÂTELIER

Became interested in the conditions

needed for equilibrium in chemical

reactions after examining some

unexpected results at a mine's furnace.

In 1888, he stated what became known as the

Le Chatelier principle: every change in one of

the factors of an equilibrium occasions a

rearrangement of the system in such direction

that the factor in question experiences a

change in the sense opposite to the original

change.

Fe 2

O 3

• C  Fe + CO 2

Fe 2

O 3

• C  Fe + CO 2

• CO

CO 2

C + CO

Fe 2

O 3

The reaction was thought to be:

Henri noticed CO was also made:

EUREKA!

The CO 2

was in equilibrium

The Equilibrium Constant and

Free Energy (K and G

o

G

o

Gibbs free energy change for all

reactants and products in standard state.

G Free energy under some other conditions.

At Equilibrium, G = 0 (no driving force)

G = G

o

+ RT ln Q

G

o

= - RT ln K

 - -32. - +6. - -20. - -33. 

• -2. - 0.
• -3. - +29.

Gibbs Free Energy Changes

Rxn# Enzyme

G°'

(kJ/mol)

1 Citrate synthase -32.

2 Aconitase +6.

3 Isocitrate dehydrogenase -20.

4

a-Ketoglutarate dehydrogenase

complex

5 Succinyl-CoA synthetase -2.

6 Succinate dehydrogenase 0.

7 Fumerase -3.

8 Malate dehydrogenase +29.

Overall free energy -57.6 kJ/mol

Biochemical Energetics