Intoduction to Physical Chemistry

The energies of chemistry is the essential point of physical chemistry. Physical chemistry is based on measurements. Although certain techniques can measure energy change like measuring heat of combustion, usually the measurement is made on concentration change which is related to energetic driving force.

Experiments may be measured at constant pressure or constant volume Total energy changeΔH (enthalpy)ΔU (energy)~E Disordered energyTΔS (entropy change) TΔS (entropy change) Ordered EnergyΔGΔA ΔH= ΔA+ TΔS ΔH= ΔG+ TΔS ΔG= ΔH- TΔSΔA= ΔH- TΔS This is the driving force for chemical change if P=constant This is the driving force for chemical change if V=constant P=constant V≠constant P ≠ constant V=constant

ΔG*ΔG* ΔGΔG A B Basicity Or Acidity Nucleophilicity Or Electrophilicity Measure of reactivity Measure of stability

The driving force for chemical change is free energy change for the reversible equilibrium ΔG and for reaction kinetics ΔG * As a result of the driving force the concentration will change and the concentration change we can calculate the magnitude of the driving force.

The three reaction mechanisms correspond to three routes on the (PES). Of course the molecular structure, the nature of the leaving group, the basicity and the concentration of the nucleophile, as well as the polarity of the solvent, will influence which route will be the most energetically favorable.