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3.14: Enthalpy of Formation

  • The enthalpy of formation is the change in enthalpy when one mole of a compound is formed from its elements in their standard states.

  • This means that when looking at how compounds are formed, we must see what the most stable form of that element is at standard temp and pressure (25 C and 1 atm), thus it equaling the standard enthalpy of formation ({delta} H subscript “f“).

  • The most stable forms of elements under standard conditions always have a standard enthalpy of formation of 0 (for example, O2 is 0, but O3 is 142.3).

  • Hess’s Law: The enthalpy change of each reaction in a series, adds up to the enthalpy change of the overall reaction.

  • When solving for enthalpy changes, if a reactant is in the product of a

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3.14: Enthalpy of Formation

  • The enthalpy of formation is the change in enthalpy when one mole of a compound is formed from its elements in their standard states.

  • This means that when looking at how compounds are formed, we must see what the most stable form of that element is at standard temp and pressure (25 C and 1 atm), thus it equaling the standard enthalpy of formation ({delta} H subscript “f“).

  • The most stable forms of elements under standard conditions always have a standard enthalpy of formation of 0 (for example, O2 is 0, but O3 is 142.3).

  • Hess’s Law: The enthalpy change of each reaction in a series, adds up to the enthalpy change of the overall reaction.

  • When solving for enthalpy changes, if a reactant is in the product of a

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