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Thermite reaction

Thermite reaction. Al 2 O 3 (s) + 2Fe(l). 2Al(s) +Fe 2 O 3 (s). H is an. Exothermic. extensive ,. State function. Hess’ Law. 2Al(s) +Fe 2 O 3 (s) Al 2 O 3 (s) + 2Fe(l). 2Al(s). + 3/2 O 2 (g).  Al 2 O 3 (s). H = -1676 kJ/mol.

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Thermite reaction

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  1. Thermite reaction Al2O3(s) + 2Fe(l) 2Al(s) +Fe2O3(s) H is an Exothermic extensive, State function Hess’ Law

  2. 2Al(s) +Fe2O3(s) Al2O3(s) + 2Fe(l) 2Al(s) + 3/2 O2(g)  Al2O3(s) H = -1676 kJ/mol _______________________________ __________ Fe2O3(s)  2Fe(s) + 3/2 O2(g) 2 Fe(s) + 3/2 O2(g)  Fe2O3(s) H= - 822 kJ/mol +  Al2O3(s) + 2Fe(s) -854 kJ/mol 2Al(s) + Fe2O3(s) 2 ( ) +15 kJ/mol 2 2 Fe(s)  Fe(l) _______________________________ __________ 2Al(s) +Fe2O3(s) Al2O3(s) + 2Fe(l) Hrxn = -824 kJ/mol

  3. Hess’ Law • Always end up with exactly the same reactants and products • If you reverse a reaction, reverse the sign of H • If you change the stoichiometry, change H

  4. Heats of formation, Hof H = heat lost or gained by a reaction “o” = standard conditions: all solutes 1M all gases 1 atm “f” = formation reaction: 1mol product from elements in standard states for elements in standard states, Hof= 0

  5. Write the equation for which Hrxn = Hof Hof for NH2CH2COOH from elements 1 mol product, in their standard states  NH2CH2COOH + O2 N2 + H2 + Cgr 2 1/2 5/2

  6. 2Al(s) +Fe2O3(s) Al2O3(s) + 2Fe(l) products reactants elements Hof 2 Al(s) Al2O3(s) 2 Al(s) 2 Fe(s) Fe2O3 2 Fe (l) 3/2 O2(g) Hof Al2O3(s) + 2 HofFe (l) Al(s) Fe2O3

  7. 2Al(s) +Fe2O3(s) Al2O3(s) + 2Fe(l) products reactants elements Hof 2 Al(s) Al2O3(s) 2 Al(s) 2 Fe(s) Fe2O3 2 Fe (l) 3/2 O2(g) Hof Al2O3(s) + 2 HofFe (l) - Hof - Hof Fe2O3 Al(s) - Hrxn = nHofproducts nHofreactants

  8. 2Al(s) +Fe2O3(s) Al2O3(s) + 2Fe(l) - nHofreactants Hrxn = nHofproducts [HofAl2O3(s) + 2 HofFe(l)] Hrxn= - [HofFe2O3(s) + HofAl(s)] 2 [(-1676) + (15)] 2 - [(-822) + 0]kJ Hrxn = = -824 kJ

  9. Bond Energies chemical reactions = bond breakage and bond formation bond energies positive energy required to break bond bond breakage (raise P.E.) bond formation (lower P.E.)

  10. Bond energies CH4 (g) + 2O2 (g)  CO2 (g) + 2H2O (g) Hrxn= bonds broken C-H 413 kJ O=O 495 kJ C=O 799 kJ O-H 467 kJ - bonds formed Hrxn= 4 [ (C-H) + (O=O)] 2 - [ (C=O) 2 + (O-H)] 4 = -824 kJ Hrxn= Hof products - Hof reactants =- 802 kJ

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