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Chemical Equilibrium, Heat, and Temperature

Chemical Equilibrium, Heat, and Temperature. Outline: Oxidation and reduction reactions Endothermic and exothermic reactions Reversible and irreversible reactions State of Equilibrium Speed of reactions Thermocouples. Sharing of electrons to form a covalent bond in the fluorine molecule.

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Chemical Equilibrium, Heat, and Temperature

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  1. Chemical Equilibrium, Heat, and Temperature

  2. Outline: • Oxidation and reduction reactions • Endothermic and exothermic reactions • Reversible and irreversible reactions • State of Equilibrium • Speed of reactions • Thermocouples

  3. Sharing of electrons to form a covalent bond in the fluorine molecule.

  4. Bonding in the O2 molecule. Outermost electrons involved.

  5. Formation of an ionic bond.

  6. Bonding in covalent SiCl4.

  7. Example of water equilibration after sudden evacuation.

  8. Example of equilibration after sudden evacuation.

  9. Recovery of equilibrium after increase in pressure.

  10. Figure 8. Typical thermocouple circuit.

  11. Figure 9. Relationship between temperature and output. Millivolts.

  12. 1940, Disappearing Filament http://www.physics.uq.edu.au/physics_museum/tour/optics.html http://astro1.panet.utoledo.edu/~ljc/Image21b.gif Figure 10. Typical optical pyrometers. Two color, fiber option http://ircon.com/web/prod/sr_series.php

  13. A liquid is in equilibrium with its vapor when the average rate of molecules leaving the liquid equals the rate joining. Equilibrium Temperature, Pressure ?

  14. Temperature, Pressure, Solute ?

  15. Melting Curve for Water http://en.wikipedia.org/wiki/File:Melting_curve_of_water.jpg

  16. For condensed phases: Temperature, Composition Pressure

  17. One mole = 6.022 x 1023 units, close to the number of carbon atoms in 12 grams of carbon http://en.wikipedia.org/wiki/File:Close-up_of_mole.jpg

  18. Oxidation and Reduction Reactions Oxidation involves loss of electrons, Reduction involves gain of electrons: OIL RIG 2Fe + O2 = 2 FeO iron loses electrons, oxidized 4 FeO + O2 = 2 Fe2O3 oxygen gains electrons, reduced Fe++ Fe+++ Mn + S = MnS Ca + S = CaS Zn + Cl2 = ZnCl2 SiO2 + 2 Ca = 2CaO + Si Ca oxidized, Si reduced

  19. C + O2 = CO2 DG0 = DH0 - T DS0 DH0 = - 169,300 Btu/ lb mole at standard conditions DH0 = - 393,000 J / mole British thermal units per pound mole: Btu/lbmol = 2.32601 J/mol

  20. C + O2 = CO2 C 2C + O2 = 2 CO (-)

  21. Reversible and irreversible reactions Reversible: NH3 + H2O = NH4OH H2O (liquid) = H2O (gas) Practically Irreversible: 4Al + 3O2 = 2Al2O3 Reactions may be irreversible when a solid or gaseous reaction product is removed. ZnO + CO = Zn (Vapor) + CO2

  22. Influencing Speed of Reactions Nature of reactants: H2 + O2vs H2 + N2 State of subdivision , surface area available Temperature Catalysis: Fe surface for 2CO = CO2 + C Concentration

  23. Le Chatelier’s Principle A system originally in equilibrium will respond to a change in temperature, pressure, or concentration in a manner reducing the change NH4OH(H2O) = NH3 + H2O Consider change in T, P, C, catalyst

  24. Heat Transfer Mechanisms: Convection Conduction Radiation

  25. Heats of Phase Change Latent heat of fusion: significant change in potential energy Latent heat of vaporization: much larger change in potential energy Heating a gram of material 1 K with no change in phase: relatively small change in kinetic energy Relative values for water

  26. Summary: A change in valance state: oxidation or reduction, OIL RIG Exothermic chemical reactions liberate heat Endothermic reactions absorb heat Reactions generally proceed to equilibrium The rate of approach depends on the nature of the reactants, their state of subdivision, temperature, catalysts, and concentration If a system in equilibrium is perturbed it responds to lessen the change Heat represents a quantity of energy Temperature represents an intensity and indicates the direction of heat transfer

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