Standard Enthalpy of Formation
This is the enthalpy change when one mole of a compound is formed from it's elements in their standard states and under standard conditions.
Standard Enthalpy of Combustion
This is the enthalpy change of one mole of a substance burned completely in oxygen under standard conditions.
Standard Enthalpy Change of Reaction
This is the enthalpy change when the reaction occurs in the molar quantities shown in the chemical equation, under standard conditions and states.
This is the heat transferred in a reaction at constant pressure. The units are kJmol-1.
Calculating Enthalpy Change
q=mcΔT q= Heat lost or gained, J. m= Mass of solution, g.
c= Specific heat capacity, 4.18 (Jg-1k-1). ΔT= Change in temperature.
In experiments mearsuring enthalpy change, use a polysyrene beaker as a container so that not much heat is gained or lost through the sides.
The total enthalpy change of a reaction is always the same, no matter which route is taken.
Average Bond Enthalpy
Enthalpy needed to break one mole of the bond, averaged over different molecules to produce gaseous atoms.
Enthalpy Formation of an Element
Enthalpy formation for an element is always zero.
Enthalpy changes of Formation
- You need to know the enthaply formation for all reactants and products that are compounds.
ΔHr + sum of ΔHf (reactants) = sum of ΔHf (products)
So, ΔHr = sum of ΔHf (products) - sum of ΔHf (reactants)