hess's law

• what is hess's law?

  enthalpy change for reaction is independent of route taken
• why is it not possible to measure enthalpy change?

  1. reaction does not occur under standard conditions
  2. activation energy is too high
  3. rate of reaction is too slow
• what are the symbols for hess's law?

  H1 - reactants

  H2 - products

  H3 - overall
• what is hess's law for enthalpy of combustion?

  H3 = H1 - H2
• what is hess's law for enthalpy of formation?

  H3 = H2 - H1
• why is hess's law more accurate than mean bond enthalpies?

  the data is specific to the bonds present for that particular reaction