Standard State
- Standard enthalpy (ΔH⁰): the enthalpy change at standard conditions
○ ⁰ = recorded in standard state
- Standard State conditions:
○ For a gas: pressure is 1 atm
○ For a pure substance in a condensed state (liquid or solid) = pure liquid or solid
○ For a solution, concentration is 1 molar
○ Temp is at exactly 25 C
- Remember:
of a pure element is 0
- Standard heats of formation: the amount of heat needed to form 1 mole of a compound from its elements in their standard states (ie. how it exists in nature → oxygen is O2)
○ Unit: kJ
○ Have to make one mole of product to meet the definition
○ SS of an element is the form in which the element exists under 1 atm and 25 C
■ Not 0 = not how the element exists in nature
- Ex: Write the equation for the formation of methanol (CH3OH)
- . Step 1: write the elements (in standard state)
● Note: The elements that exist as diatomic molecules are hydrogen (H2), nitrogen (N2), fluorine (F2), oxygen (O2), iodine (I2), chlorine (Cl2) and bromine (Br2)
2. Step 2: Balance 
- Formula:
(on RFS)
○ Use chart → add up all of heats of formation of products – all the heats of formation of reactants