Chemical Equilibrium–Study Guide


Learning Objectives and Key Terms

Key Terms and ideas you should know

  • Law of mass action
  • Dynamic equilibrium
  • Homogenous equilibrium with examples
  • Write equilibrium constant expressions for the equations provided
  • Heterogeneous equilibrium and examples
  • Write equilibrium constant expressions for heterogeneous equilibria
  • Difference between concentration quotient and equilibrium constant Qc Vs Kc
  • Factors affecting chemical equilibrium: need to elaborate each
    • Concentration
    • Change in Pressure / Volume for gaseous reactants
    • Temperature
    • Addition of a catalyst
    • Addition of an inert gas
  • Le Chatliers principle definition
  • Predicting shift in equilibrium based on the variation of concentration, temperature, pressure / volume change all possible combinations. One example for each type of shift like
    • Adding a reactant
    • Adding a product
    • Removing a reactant
    • Removing a product
    • Adding heat to an exothermic / endothermic reaction
    • Taking away heat from an exothermic / endothermic reaction
    • Adding an inert gas without change in volume / with change in volume
  • Values of Kc and its implication
    • What does it mean if the value of Keq is very large / very small / = 1
    • What will the value of Kc be if the reaction is reversed
    • What happens to the value of Kc if the equation is multiplied by a coefficient
    • Relation between Kc and Kp
  • Problems
    • Determining molar concentrations of reactants and products
    • Generate an ICE table to calculate equilibrium concentrations
    • Determine value of Kc form equilibrium concentrations
    • Find the equilibrium concentration if the equilibrium constant is given
    • Find the equilibrium concentration of one of the reactants in a reaction when the equilibrium expression is a perfect square.
    • Find the equilibrium concentration when the equilibrium constant is given and the equilibrium expression is NOT a perfect square; you will use the quadratic equation.
    • Determine the new equilibrium concentrations of reactants when a stress is applied by adding a known quantity of reactant. Problems on Le Chatliers Principle.
    • Predicting the quantity of a reactant needed to obtain a known increase in the concentration of one of the products. Le Chatliers principle.
    • Predicting concentrations of reactants or products when Kc is known and the value of Kc is small – using the 100th rule.
    • Problems converting Kc to Kp and Vice Versa

Spontaneity of Chemical Reactions

  • Define spontaneity
  • Define Entropy
    • Predicting entropy of chemical reactions using states of matter, number of entities and temperature changes.
  • Significance of free energy
    • Predicting spontaneity based on values of free energy
    • When free energy or \Delta G = O
    • When free energy or \Delta G = < O or negative
    • When free energy or \Delta G = > O or positive
  • Relationship between \Delta G and equilibrium constant \Delta G = -RTlnKc or \Delta G = -RTln Kp, ln can be changed to log but multiply by 2.303 appropriately
  • Gibbs-Helmholtz equation\Delta G = \Delta H -T\Delta S
  • Predicting spontaneity based on values provided
  • Why can’t Kc have a negative value?
  • What is the effect of the presence of a catalyst on equilibrium constant?
  • Predict the temperature at which a reaction would become spontaneous. Using Gibbs-Helmholtz equation, assumption is that the system is at equilibrium, then calculate the temperature ‘T’

Web Links

Chemical Equilibrium

1. Wikipedia

2. ThinkQuest

3. Shodor

Law of Mass Action

1. Wikipedia

2. University of Waterloo

Reaction Quotient

1. Reaction Quotient

2. Chem1

3. Purdue University

Equilibrium Constants

1. Chemguide

2. Wikipedia

3. Purdue University

Haber Process

1. Aus-e-tute

2. Haber – Process

3. Chemguide