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Thermochemistry Introduction

Thermochemistry Introduction. E. A. Mottel Integrated, First-Year Curriculum in Science, Engineering and Mathematics. Please be sure you have a copy of Thermochemistry - Introduction lecture notes Chemical Reactions Problem Set. Chemical Thermodynamics.

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Thermochemistry Introduction

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  1. ThermochemistryIntroduction E. A. Mottel Integrated, First-Year Curriculum in Science, Engineering and Mathematics

  2. Please be sure you have a copy of Thermochemistry - Introduction lecture notes Chemical Reactions Problem Set.

  3. Chemical Thermodynamics • A study of the energy changes which accompany the physical and chemical changes of matter. • Net heat flow • conservation of energy • Terms • heat, work, internal energy and enthalpy

  4. Chemical Reactions • Requires knowledge of the chemical nature of the reactants and products. • Formula, phase, solubility, ionic character. • Equations corresponding to these processes should be balanced and completely annotated (g, l, s, aq).

  5. H2O NH4NO3(s) endothermic enthalpy of solution H2O H2SO4(conc) Solution ReactionsExamples NH4+(aq) + NO3–(aq) Complete the reaction DHsoln = +25.8 kJmol–1 2 H+(aq) + SO42–(aq) Complete the reaction DHsoln = -96.2 kJmol–1 exothermic

  6. H2O(l) H2O(g) H2O(s) H2O(s) H2O(g) H2O(l) Changes in Physical StateWrite an appropriate equation for each of the following processes Enthalpy of vaporization of water Enthalpy of sublimation of ice Enthalpy of fusion of water

  7. (NH4)2Cr2O7(s) Cr2O3(s) + N2(g) + 4 H2O(g) 2 NaI(aq) + Cl2(g) 2 NaCl(aq) + I2(aq) HCl(aq) + NaHCO3(s) NaCl(aq) + H2CO3(aq) Chemical ReactionsExamples Decomposition Single replacement Double replacement

  8. C2H5OH(l) + 3 O2(g) 2 CO2(g) + 3 H2O(g) carbon is converted to hydrogen is converted to 2 Na(s) + C(gr) + 3/2 O2(g) Na2CO3(s) most common elemental form Chemical ReactionsExamples Combustion Formation

  9. C12H22O11(s)+ 12 O2(g) 12 CO2(g) + 11 H2O(g) 12 C(gr) + 11 H2(g) + 11/2 O2(g) C12H22O11(s) FeS(s)+ 3/2 O2(g) SO2(g) + FeO(s) Ni(s) + N2(g) + 3 O2(g) Ni(NO3)2(s) Combustion and FormationWrite an appropriate equation for each of the following processes Combustion of sucrose (C12H22O11) Formation of sucrose Combustion of iron(II) sulfide to form sulfur dioxide Formation of nickel(II) nitrate

  10. Thermodynamic Terms • Heat, q. • Work, w. • Internal energy, E or U • System • Surroundings • Enthalpy, H • State Functions

  11. Heat • Thermal energy - heat flows form a warmer body to a cooler body. q distinction between heat and temperature Are these intensive or extensive properties?

  12. F F F F F F F F F F F F F F F F F F F F F F F F d Work • Work must have an intensive and capacitive factor, or no work is done w = F·d distinction between work and "being tired".

  13. potential amount of electricity (charge) difference Work Type of Work Intensity Capacity mechanical force distance expansion pressure volume change (dV) electrical gravitational gravity x height mass

  14. Internal Energy • The total energy (E or U) of a molecule or ion is due to all sources of energy. • Molecular motion (kinetic energy) • Chemical bonding (potential energy)

  15. translation Molecular Motion rotation vibration

  16. Potential Energy • electronic • electron energy levels • bonding

  17. First Law of Thermodynamics • The change in internal energy of a system is equal to the energy added to the system, minus the energy lost by the system. DU = energygained - energylost

  18. System • Any region of space or material which is considered in dealing with energy changes that matter undergoes. • Closed system - system that does not exchange matter with the surroundings. • Isolated system - system that does not exchange matter or energy with the surroundings.

  19. Surroundings • Everything else except the system (the rest of the universe).

  20. Enthalpy • H = E + PV. • The total energy content of a molecule. • internal molecular motion. • electronic energy released due to bonding. • pressure-volume work required to maintain the volume of the molecule. • Only defined for a constant pressure process.

  21. State Functions • Depend only on the initial and final conditions • not the pathway of the process. • Change in the function is indicated by D, final - initial. • Often denoted by a capital letter. • Examples: P, V, T, E, H. • Non-state functions examples: q, w.

  22. State Functions • Examples of work performed by a gas: • Expansion of a gas against a constant external force (Pext = constant). • Expansion of a gas against a changing external force (Pext = Pgas). • Increase in pressure of a gas in a rigid container (DP > 0).

  23. Internal Energy • The total energy (E or U) of a molecule or ion is due to all sources of kinetic and potential energy translation rotation

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