CHEM 433 – 9/9/11 I.Introductory Topics B. Molecules and Energy (Ch. 0) - Definitions & Introductory comments - Energy Units - How do molecules Store energy? —> Quantization Read: Chapter “0” HW DUE Th – but start sooner than later.

Basic Definitions re: “Molecules and Energy” Working Definition of Physical Chemistry: “ The study of the physical properties of matter, how these affect chemical change, and the interplay of energy with matter. ” Matter: Atoms and molecules (also p +, n°, e -, quarks?, and all other “ stuff ” – anything w/ mass). Substance: A pure distinct form of matter. (i.e. all the atoms/ molecules are the same). Mole(s): Unit used to specify the amount of a substance (n).

Basic Definitions re: “Molecules and Energy” Avagadro Constant (N A ): 6.02…x10 23 mol -1 ; —> The number of C atoms in exactly 12 g of 12 C. Intensive Properties are independent of n. (P, T, Density…). Extensive Properties depend on n. (V, mass, entropy…). (failure to understand the difference can have disastrous consequences: ) Molar Properties: Extensive properties made to be intensive via division by n, i.e. (X m = X/n). Note: Only intensive properties can be characteristic. Energy: Capacity to perform work. **** Is energy intensive or extensive?

How much energy is a C-C bond “worth” ? (i.e. how much energy is required to break it?) CC ~350 kJ/mol What is the value in…. kcal/mol ? J ? eV? cm -1 ? 83 kcal/mol 5.8 x J 3.6 eV 29,000 cm -1

Energy Quantization: The general Idea is that the smaller the particle, and the more tight its confines are, the larger the SPACINGS between ENERGY LEVELS… E Puck in a rink Nuclei held by bonds e – held by nuclei  E >>> kT i.e. large  E ≥ kT  E ~ 0