Enthalpies of Formation + Hess' law

Standard Enthalpy of Formation (ΔH°_f)

• at SATP, elements exist in a preferred form, called the standard state

• Formation energy for 1 mole of compound from elements (O₂ must be ½ in making H₂O)

Elements have how much standard enthalpy of formation?

ΔH°_f = 0 kJ/mol in standard state

Enthalpy is a state function, what does this mean

Depends on the current state of the system, not on the way in which the system acquired that state

Hess’s Law

energy change for any chemical or physical process is independent of the pathway or number of steps required to complete the process ONLY IF the reaction conditions remain constant