CH110

Chapter 14 Notes

We are skipping Chapter 13 on kinetics, which you will cover next semester in P.Chem.

We have metioned dynamic equilibrium several times before, and now explore the topic in detail

In an equilibrium, the forward and reverse processes are occuring at the same rate

Reactant and product concentrations are constant

The dynamic nature of an equilibrium (eq) can be demonstrated using radioactive tracers (why?)

Equilibrium constants

Product concentrations divided by reactant concentrations gives the equilibrium constant expression or equation

ex for 2 NO (g) + O₂ (g) in eq. with 2 NO₂ (g), K_c = [NO₂]² / [NO]² [O₂] = 4.67 x 10¹³

exponents equal the stoichiometric coefficients

given some of the variables, you can solve for the missing one

Reaction rates at equilibrium

For the reaction above, the forward rate = k_f[NO]² [O₂] where k is the rate constant a chapter 13 proportionality constant which relates rate to concentration (appearance of products or disappearance of reactants)

The reverse rate = k_r[NO₂]²

At eq, forward rate = reverse rate

So, the equilibrium constant K_eq = k_f / k_r

Effect of reversing equation or multiplying whole system by a number

Partial pressures can be used in place of concentrations for gas equations (K_p)

Pure solids and liquids DO NOT appear in equilibrium constant expressions since their CONCENTRATIONS don't change during the reactions (AMOUNTS of course change, but not concentrations)

Extreme values for K indicate non-reversible reactions

Reaction quotient

An examination of the K type for a reaction NOT at eq

LeChatelier's Principle

A stress placed on a reaction system is minimized

Addition of products or removal of products

Changing pressure (see Fig. 14.5)

Changing temperature

Addition of catalyst