Bài giảng hóa bằng tiếng anh Chemical Equilibrium

Hemoglobin • protein Hb found in red blood cells that reacts with O2 enhances the amount of O2 that can be carried through the blood stream Hb + O2  HbO2 the Hb represents the en

Chemical Equilibrium

Hemoglobin

• protein (Hb) found in red blood

cells that reacts with O2

enhances the amount of O2 that

can be carried through the blood

stream

Hb + O2  HbO2

the Hb represents the entire protein

– it is not a chemical formula

the  represents that the reaction

is in dynamic equilibrium

Hemoglobin Equilibrium System

• the concentrations of Hb, O2, and HbO2 are all

interdependent

• the relative amounts of Hb, O2, and HbO2 at

equilibrium are related to a constant called the

equilibrium constant, K

 the larger the value of K, the more product is found at

equilibrium

• changing the concentration of any one of these

necessitates changing the other concentrations to

reestablish equilibrium

O 2 Transport

in the lungs, with high

concentration of O2, the

equilibrium shifts to

combine the Hb and O2

together to make more

HbO2

in the cells, with low

concentration of O2, the

equilibrium shifts to

break down the HbO2

and increase the amount

in lungs

in cells

HbF

Hb

Fetal Hemoglobin, HbF

• fetal hemoglobin’s

equilibrium constant is

larger than adult

hemoglobin

• because fetal hemoglobin

is more efficient at

binding O2, O2 is

transferred to the fetal

hemoglobin from the

mother’s hemoglobin in

the placenta

Oxygen Exchange between

Mother and Fetus

Reaction Dynamics

• when a reaction starts, the reactants are consumed and

products are made

 forward reaction = reactants  products

 therefore the reactant concentrations decrease and the product

concentrations increase

 as reactant concentration decreases, the forward reaction rate

decreases

• eventually, the products can react to reform some of the

reactants

 reverse reaction = products  reactants

 assuming the products are not allowed to escape

 as product concentration increases, the reverse reaction rate increases

• processes that proceed in both the forward and reverse

direction are said to be reversible

 reactants  products

Hypothetical Reaction

Time [Red] [Blue]

0 0.400 0.000

10 0.208 0.096

20 0.190 0.105

30 0.180 0.110

40 0.174 0.113

50 0.170 0.115

60 0.168 0.116

70 0.167 0.117

80 0.166 0.117

90 0.165 0.118

100 0.165 0.118

110 0.164 0.118

120 0.164 0.118

The reaction slows over time,

At some time between 100 and 110 sec,

equilibrium has been established

Notice that equilibrium does not mean

that the concentrations are equal!

Once equilibrium is established, the rate

Hypothetical Reaction

Concentration vs Time for 2 Red > Blue

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 20 40 60 80 100 120 140

Time, sec

[Red]

[Blue]

Reaction Dynamics

Rate Forward Rate Reverse

Dynamic Equilibrium

reaction accelerates, eventually they reach the same rate

• dynamic equilibrium is the condition where the

rates of the forward and reverse reactions are equal

concentrations of all the chemicals remain constant

because the chemicals are being consumed and

made at the same rate

H 2 (g) + I 2 (g)  2 HI(g)

at time 0, there are only reactants

in the mixture, so only the forward reaction can take place

at time 16, there are both reactants and products in the mixture, so both the forward reaction and reverse reaction can take place

H 2 (g) + I 2 (g)  2 HI(g)

at time 32, there are now more products than reactants in the mixture − the forward reaction has slowed down as the reactants run out, and the reverse reaction accelerated

at time 48, the amounts of products and reactants in the mixture haven’t changed – the forward and reverse reactions are proceeding at the same rate – it

H 2 (g) + I 2 (g)  2 HI(g)



Since the [HI] at equilibrium

we say the position of equilibrium favors products

As the reaction proceeds,

and the [HI] increases

And since the

product

concentration is

increasing, the

reverse reaction

rate speeds up

Once equilibrium is established, the concentrations

no longer change

Equilibrium  Equal

• the rates of the forward and reverse reactions are

equal at equilibrium

• but that does not mean the concentrations of

reactants and products are equal

• some reactions reach equilibrium only after almost all the reactant molecules are consumed – we say

the position of equilibrium favors the products

• other reactions reach equilibrium when only a

small percentage of the reactant molecules are

consumed – we say the position of equilibrium

favors the reactants

An Analogy: Population Changes

When Country A citizens feel overcrowded, some

will emigrate to Country B

An Analogy: Population Changes

However, as time passes, emigration will occur in

both directions at the same rate, leading to

populations in Country A and Country B that are

constant, though not necessarily equal