A few words about the difference between thermodynamics and kinetics:

Keq is an equilibrium constant. It has nothing to do with kinetics, it is a thermodynamic term. Kinetics determines the rates of reactions, how fast they reach equilibrium, not what the equilibrium conditions are.

Thermodynamics:

G'= the Gibb's free energy for a reaction under standard conditions. Does the equilibrium favor products (positive value) or the reactants (negative value). These values are determined under standard conditions: 25'C, 1 atm, and all reagents at 1M, except [H]=1 x 10-7. This standard condition value is then used to determine what will happen under physiological conditions, ie: not all of the reactants are at 1M in the body! The free energy of a reaction determines whether products or reactants will be favored, and whether there is energy available to do work.

Kinetics:

Remember the rule: a 10 fold rate increase corresponds to a 5.7 kj/mole (1.36 kcal/mol) difference in activation energy. You may want to practice prooving that for yourself. (I can envision an exam question in your future.)

Sample question:

Design a quantitative assay for lactate dehydrogenase (LDH). This enxzyme catalzyes the following reaction:
Pyruvate + NADH + H+ ----------------> lactate + NAD+
NADH absorbs light at 340 nm, NAD+ does not. This enzyme is released from injured cardiac muscle cells, and thus high blood levels of LDH are indicative of a a myocardial infarction.

To design an assay to determine the amount of LDH present, you need to generate a standard curve. Plot something vs enzyme concentration. You will generate a straight line with y= mx +b. The y is your something values, the x is your enzyme concentrations, m is the slope and b is the y intercept. Then measure the "something" of your unknown and use the graph that you generated to determine the unknown enzyme concentration, using the equation of the line on your standard curve.

Now, what is the something? What is related to enzyme concentration? Is substrate concentration? Is Km? No. But, Vmax is! More enzyme, more velocity! How can you be assured that the velocity of a reaction is the Vmax? By measuring the velocity at a substrate concentration that is above the Km, you can be assured that the enzyme is saturated, and that the enzyme is at maximum velocity.

So, measure vo at various enzyme concentrations, using a substrate concentration that is well above the Km. (First you will need to determine Km by measuring the initial velocity (vo) at various substrate concentrations and plotting 1/vo vs 1/[S].) Then make a standard curve of vo vs [enzyme]. Next measure the vo of the unknown, use the measured vo and the equation of the line to calculate the unknown enzyme concentration.

How are you going to measure vo? By determining the rate at which NADH disappears, you can measure the rate of the reaction. LDH converts NADH to NAD, NADH absorbs at 340nm, NAD does not. Measuring the 340nm absorbance decrease as a function of time will give the reaction rate.