When the reaction is written as above the equilibrium constant, K_eq, is an "association constant", K_a. When the equation is written in the reverse orientation, the equilibrium constant, K_eq, is a "dissociation constant", K_d.

The A-B Bond Energy is ΔG° (Δ is the Greek letter meaning "change",) and the relationship between ΔG° and the equilibrium constant, K_eq, is:
ΔG° = -R T ln K_eq

R is the Gas Constant of 1.987 cal/degree-mole
T is the Temperature in Kelvin (= °C + 273)
RT = 592 cal/mole at 25 °C

Solving the above for K_eq:         K_eq = exp(-ΔG°/RT)

Choose the type and number of bonds:	1 H bond, -1 Kcal/mole 2 H bonds, Total = -2 Kcal/mole 5 H bonds, Total = -5 Kcal/mole 10 H bonds, Total = -10 Kcal/mole 20 H bonds, Total = -20 Kcal/mole 30 H bonds, Total = -30 Kcal/mole 40 H bonds, Total = -40 Kcal/mole 50 H bonds, Total = -50 Kcal/mole 1 ionic bond, Total = -10 Kcal/mole 2 ionic bonds, Total = -20 Kcal/mole 5 ionic bonds, Total = -50 Kcal/mole 1 covalent bond, -100 Kcal/mole
Choose the equilibrium concentration for AB	[AB] = 1 molar [A = [B] = 100 millimolar [A = [B] = 10 millimolar [AB] = 1 millimolar [AB] = 100 micromolar [AB] = 10 micromolar [AB] = 1 micromolar
Having made the choices above - click

The equilibrium is between the two molecules A, B and the molecule AB, in which A and B are held together by the bond(s) chosen above. The display shows the number (rounded to the nearest integer) of molecules of AB which are present for each molecule of A (or of B, since [A] = [B].)