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Spontaneous Processes

Objectives:

Key Terms:

Notes: (23-1)

Chemical reactions occur around us at all times throughout day.  Some require heating and some require catalysts and enzymes.  Still some require no intervention at all and just seem to happen on their own.  These reactions are called spontaneous reactions.

spontaneous reactions proceed without outside intervention
enthalpy is negative (-DHo)
exothermic
equilibrium constant is much greater than 1 (Keq >> 1)
Have very low activation energies
all explosive reactions are spontaneous

The rusting of a nail is a common example of a spontaneous reaction.  It occurs in the presence of oxygen, sunlight and water and proceeds whether we want it to or not.

                4Fe (s) + 3O2 (g) g 2Fe2O3(s)        -DHo = -1644kJ 

The three fundamental questions asked by chemists studying spontaneous reactions are:

  1. How rapidly does the reaction take place?
    depends on the activation energy - energy needed to start the reaction
    depends on the temp., surface area, and catalysts present
    catalyst lower the activation energy required to start a chemical reaction
  2. Will all the reactants turn to products
    dependant on the equilibrium constant - the greater the constant the the greater the percentage of products compared to reactants
     
  3. What is the direction of the spontaneous reaction
    this must be initially determined in order to calculate and understand the first two questions
    dependant on the study of thermo dynamics - is the study of how heat and work effects the and accompany all changes in matter
 

 

Last modified: May 19, 2003