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Physical Chemistry

Physical Chemistry. Dónal Leech donal.leech@nuigalway.ie Ext 3563 Room C205, Physical Chemistry. Notes for downloading (powerpoint and word) http://www.nuigalway.ie/chem/Donal/Teaching.htm. Chemistry. Physical Sciences Sub-atomic Atoms Materials Atmosphere Stellar.

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Physical Chemistry

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  1. Physical Chemistry Dónal Leech donal.leech@nuigalway.ie Ext 3563 Room C205, Physical Chemistry Notes for downloading (powerpoint and word) http://www.nuigalway.ie/chem/Donal/Teaching.htm

  2. Chemistry • Physical Sciences • Sub-atomic • Atoms • Materials • Atmosphere • Stellar • Biological Sciences • Organisms • Organs • Tissues • Cells • DNA Chemistry • Molecules • Bonds • Forces Molecular Sciences

  3. Physical Chemistry Establishes and develops the principles that are used to explain and interpret the observations made in chemistry Bulk  Individual  Rates Thermodynamics   Chemical reactions Quantum mechanics & spectroscopy Equilibrium  Structure  Change ENERGY

  4. Textbook • Brown, LeMay, Bursten • Chemistry: The Central Science, 9th Edition Companion Web-site http://www.prenhall.com/brown

  5. Dynamic EquilibriumChapter 15 Example liquid + heat vapour an endothermic physical change

  6. Le Chatelier’s Principle • When a dynamic equilibrium is upset by a disturbance, the system responds in a direction that tends to counteract the disturbance and, if possible, restore equilibrium liquid + heat vapour Increase the temperature (add heat)

  7. Le Chatelier’s Principle • When a dynamic equilibrium is upset by a disturbance, the system responds in a direction that tends to counteract the disturbance and, if possible, restore equilibrium vapour liquid + heat  Liquid evapourates to absorb the added heat and the position of the equilibrium shifts to the right

  8. Solution of a Weak Acid CH3COOH + H2O H3O++CH3COO- For a given composition of a system, equilibrium is independent of which side you approach it from…..reactions are REVERSIBLE N2O4(g)  2NO2(g) Cinit 0.0350 mol 0 or 0 0.0700 mol Cequil 0.0292 mol 0.0116 mol

  9. Equilibrium Lawsimple relationship between molar concentrations (or pressures) of reactants and products at equilibrium H2(g) + I2(g)  2HI(g) (at 440C) Mass action expression: Where Q is the reaction quotient LAW: at equilibrium the reaction quotient is equal to the equilibrium constant, K. In general for dD + eE  gG + hH

  10. Heterogeneous Equilibria(involving more than one phase)

  11. Equilibrium Law for Gaseous Reactions For gaseous reactions use partial pressures, P, to give an equilibrium constant (Kp)

  12. Predicting direction of equilibrium changes(Le Chatelier redux) Adding or removing reactant or product Cu(H2O) 42+(aq.) + 4Cl-(aq.) CuCl 42-(aq.) + 4H2O Changing volume (or pressure)-gases only as liquids and solids are incompressible Decrease V=>increase P System opposes this by reducing the number of molecules

  13. Predicting direction of equilibrium changes(Le Chatelier redux) Changing temperature (heat) System opposes this by trying to absorb the added heat ONLY factor that actually changes the value of K Effect of catalyst Speeds up approach to equilibrium, but does not alter K or the system (kinetics)

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