Kinetics :  Activation Energy

Activation Energy (Ea) - The energy level that the reactant molecules must overcome before a reaction can occur
Endothermic Reaction

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 In an endothermic reaction in which
the change in enthalpy between the
products and the reactants is positive,there must be an extra input of energy above the energy level of the products in order for a reaction to occur.
Exothermic Reaction

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 Even in an exothermic reaction in which
the change in enthalpy between the products
and the reactants is negative, there must be
an input of energy to start the reaction.


 
Arrhenius Equation
  
By rearranging this equation, it can be used to determine the activation energy of a reaction.

This equation is in the form: 

Arrhenius Equation

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   When the lnk (rate constant) is plotted versus the
inverse of the temperature (kelvin), the slope is a
straight line.  The value of the slope (m) is equal
to -Ea/R where R is a constant equal to 8.314 J/mol-K.
When the equation of the slope is rearranged: 

Next:  "Integrated Forms of the First-Order and Second-Order Rate Laws"