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Enthalpy
Objectives:
Key Terms:
Notes: (23-2)
Chemical reactions will always try to reach their lowest energy state. This low energy state relates to the chemical's minimum potential energy. The enthalpy (DH) is the numerical representation of the potential energy of the of the products compared to the potential energy of the reactants.
 | DH for an endothermic reaction is positive |
| DH for an exothermic reaction is negative |
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After the activation energy has been generated, most spontaneous reactions are exothermic. The energy required to move the reaction forward is provided by the formation of the new bonds.
| reactions
that generate a large amount of heat are always spontaneous
| ||
| Not
ALL spontaneous reactions are exothermic
|
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Gibbs Free Energy
Because not all exothermic reactions are spontaneous, an American mathematician named J. Willard Gibbs related enthalpy and entropy to determine whether reactions would be spontaneous or not. The information was related in the Gibbs Free Energy equation.
DG = DH - TDS
| If DG is negative, the reaction is spontaneous |
| If DG is positive, the reaction is not spontaneous and requires additional energy to proceed |
| If DG is zero, the reaction is at equilibrium |