Equilibrium

Question 1

Rate of forward reaction:

Answer 1

rf = kf [A][B]

Initially none of the reaction products C and D are present. No reaction takes place in the reverse direction. The only
reaction, initially, is in the forward direction.

Question 2

Rate of reverse reaction:

Answer 2

rb = kb [C][B]

As the reaction proceeds, [A] and [B] decrease, and [C] and [D] increase. The rates of the forward and reverse reactions respond as follows

Question 3

When the rate of the back reaction becomes equal to the rate of the forward reaction…

Answer 3

the [A], [B], [C], and [D] no longer change and the system is said to have attained chemical equilibrium

Question 4

dynamic equilibrium:

Answer 4

Although it would appear that no further change takes place once the system has reached equilibrium, be aware that at the molecular level the following two reaction processes take place continuously. There does not appear to be any change taking place because the two processes take place at exactly the same rates.

Question 5

equilibrium constant:

Answer 5

-The constant K is called the equilibrium constant of the
reaction.

• in deriving this expression we have assumed that the reaction of interest is an elementary reaction in both directions. However, it turns out that the above expression holds true for ANY chemical reaction (whether elementary or complex).

Question 6

In 1864 GULDBERG and WAAGE postulated the now famous…

Answer 6

LAW OF MASS ACTION. According to the law of mass action:

Any reversible chemical reaction will have associated with it an
equilibrium constant.

Applies irrespective of whether the reaction is elementary or complex.

Question 7

The magnitude of equilibrium constants:

Answer 7

The magnitude of the equilibrium constant gives information about what we could expect the reaction mixture to look like at equilibrium.

Question 8

If Kc =1 then …

Answer 8

we would expect that, when the system has reached equilibrium [C] , [D] = [A] , [B]. The equilibrium
mixture will contain significant amounts of all the reactants and products

Question 9

If Kc >1 then we would expect that,

Answer 9

when the
system has reached equilibrium [C] , [D]&raquo_space; [A] , [B]. The equilibrium mixture will contain much more
product than reactant. The position of equilibrium is said to be far to the right.

Question 10

If Kc < 1 then we would expect that,

Answer 10

when the
system has reached equilibrium [C] , [D] &laquo_space;[A] , [B]. The equilibrium mixture will contain much more
reactant than product. The position of equilibrium is said to be far to the left.

Question 11

In vitro / In vivo

Answer 11

-Isolated enzyme: measure in vitro Keq

Measure reactants in vivo in whole tissue to calculate a mass action ratio: M.A.R.

• Both = Measures of A,B,C, and D
• Compare: Keq versus MAR
• Enzyme step is at Equilibrium in cells if
  Keq = MAR
• Enzymes NOT at Equilibrium:
  –> are flux generating enzymes in vivo !