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CHEM 433 – 9/9/11

CHEM 433 – 9/9/11. 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”.

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CHEM 433 – 9/9/11

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  1. CHEM 433 – 9/9/11 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.

  2. 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).

  3. Basic Definitions re: “Molecules and Energy” • Avagadro Constant (NA): 6.02…x1023 mol-1; • —> The number of C atoms in exactly 12 g of 12C. • 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: http://www.youtube.com/watch?v=zrzMhU_4m-g ) • Molar Properties: Extensive properties made to be intensive via division by n, i.e. (Xm = X/n). • Note: Only intensive properties can be characteristic. • Energy: Capacity to perform work. • **** Is energy intensive or extensive?

  4. How much energy is a C-C bond “worth” ? (i.e. how much energy is required to break it?) ~350 kJ/mol C C What is the value in…. kcal/mol ? J ? eV? cm-1? 83 kcal/mol 5.8 x10-19J 3.6 eV 29,000 cm-1

  5. 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 E ~ 0 E ≥ kT E >>> kT i.e. large Puck in a rink Nuclei held by bonds e– held by nuclei

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