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Introduction to Molecules and Energy in Physical Chemistry

This introductory chapter discusses fundamental definitions and concepts in physical chemistry related to molecules and energy. It covers the study of physical properties of matter, quantization of energy, Avogadro's constant, intensive versus extensive properties, molar properties, and energy quantization in small particles. The text explores the capacity of energy to perform work, the value of a C-C bond in various energy units, and the idea of energy quantization in particles with confined spaces.

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Introduction to Molecules and Energy in Physical Chemistry

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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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