# Equilibrium Constant from Thermodynamic Parameters

Write the equilibrium -constant expression and calculate the value of the equilibrium constant for each of the follow reactions at 298 K, using data from Appendix C. ** Appendix C is in the Chemistry: The Central Science 11e textbook. It is a chemistry 100 (first year book). The Appendix contains delta Hf, delta Gf and S at 298.15K for selected substances.

a) H2 (g) + I2 (g) <--> 2 HI (g)

b) C2H5OH (g) <--> C2H4 (g) + H2O (g)

c) 3 C2H2 (g) <-> C6H6 (g)

#### Solution Preview

(a) Reaction under consideration:

H2 (g) + I2 (g) <--> 2 HI (g)

To write an equilibrium expression for any chemical equation, multiply the concentration (or partial pressure) of the species on the product side raise to the power of their coefficients and divide by the same treatment with the species on the reactant side.

Please see attached Word file for the equilibrium expression written for the above reaction both in terms on concentrations and partial pressures.

Since no information is given about the concentrations or pressures at equilibrium, the equilibrium expression cannot be used to find the value of the equilibrium constant (K). To get the actual value of K we need ...

#### Solution Summary

The equation relating the equilibrium constant (K) and the free energy change for a chemical reaction is derived using thermodynamic relationships. This equation is used to calculate the value of the equilibrium constant for three specific reactions using standard tabulated thermodynamic quantities. The solution also includes the calculation of free energy change for a chemical reaction from the tabulated free energy of formations. The attached Word file contains step-by-step procedure for these calculations.