Thermochemistry

1. Thermochemistry Dr. Ron Rusay

2. Energy Joules (J) / calorie (cal) : (4.184 J = 1 cal) • Can be defined as the capacity to do work. • Chemical energy is defined as heat. • Name five other types of Energy.

3. Two Types of Energy • Potential: due to an object’s position or material’s composition - which can be converted to work • Kinetic: due to motion of an object • KE = 1/2 mv2 • (m = mass, v = velocity)

5. Law of Conservation of Energy • Different forms of energy can be inter-converted but can neither be created nor destroyed. • (Euniverse is constant) • Describe three inter-conversions of energy.

6. Temperature v. Energy • Temperature reflects random motions of particles; i.e. the kinetic energy of a system. • Heat involves a transfer of energy between 2 objects due to different energies and temperature differences.Always: HOT cold

7. Heat (Energy) Loss

8. Energy: A State Function • Depends only on the state of the system - not the path of how it arrived at that state. • It is independent of pathway.

9. System and Surroundings • System: That on which we focus attention • Surroundings: Everything else in the universe • Universe = System + Surroundings

11. Defining Energy ChangeExo- and Endo- thermic(Exergonic and Endergonic) • Two types of energy change : • Exothermic: Heat flows outof the system (to the surroundings).…negative sign • Endothermic: Heat flows intothe system (from the surroundings).…positive sign

12. First of Three Laws of Thermodynamics • First Law of Thermodynamics: The energy of the universe is constant or “energy is conserved”.

13. Heat Capacity(Specific Heat) P O http://chemconnections.org/general/chem120/Flash/specific_heat_s.swf

14. Terminology • Specific heat capacity heat capacity per gram = J/°C g or J/K g • Molar heat capacity heat capacity per mole = J/°C mol or J/K mol

15. Calorimeters http://chemconnections.org/general/chem120/Flash/calorimetry_s.html

16. QUESTION

17. Heat Capacities

18. QUESTION

19. Why can you burn the top of your mouth with hot pizza and not the bottom? (The top & bottom are at the same temperature!) http://www.dailymotion.com/video/x3hfwx_the-science-of-pizza_people

20. Why can you burn the top of your mouth with hot pizza and not the bottom? (The top & bottom are at the same temperature.) (Cp) on body fat. In obese mice (fat content 52.76% body wt) the heat capacity was 2.65 kJ kg-1 K-1 and in lean mice (fat content 7.55% body wt) the heat capacity was 3.66 kJ kg-1 K-1.

21. Specific Heat Interactive

22. Energy diagrams w = - 1500 kJ q = +2000 kJ E  = q + w = +2000kJ + (-1500kJ) = +500kJ Can the system do 3000 kJ of work on the surroundings? Process Path If a system has 2,000 kJ put into it and the system does work of 1500 kJ on the surroundings, what is ?

23. Energy diagrams w = - 3000 kJ q = +2000 kJ E Process Path Can the system do 3000 kJ of work on the surroundings?

24. QUESTION

26. QUESTION

28. EnergyThe Gas Combustion Engine http://chemconnections.org/general/movies/html-swf/workversusenergyflow.htm

30. Enthalpy diagramsqp = H H2O (l) @ 25 oC H H = ? H2O (s) @- 25 oC Process Path If 50.0 g of ice @ -25 oC warms to 25 oC what is H of the process?

31. http://chemconnections.org/general/movies/HeatingCurves.swf

32. Hdeposition= (-) H = J or kJ cal or kcal Hcondensation= (-) Hsolidification= (-) f.p. oC cooling cooling heating heating b.p. oC m.p. oC Hvaporization= (+) Hfusion= (+) Hsublimation= (+)

33. Enthalpies H?s  l  g H2O (l) @ 25 oC H = Cp liq x mass x T H H2 O (l) @ 0 oC Hfusion = 6.009 kJ/mol H2 O (s) @ 0 oC H2 O (s) @- 25 oC H = Cp ice x mass x T Process Path H = Hice +Hfusion +Hliq If 50.0 g of ice @ -25 oC warms to 25 oC what is H of the process? H = ?

34. QUESTION

35. “Heat of Reaction” Change in Enthalpy http://chemconnections.org/general/movies/hesslaw.mov • The heat of any reaction can be calculated from enthalpies of formation of reactants and products.(“Hess’s Law”) • Hrxn° = npHf(products) nrHf(reactants)

36. QUESTION • 4675 kJ B) -1545 kJ C) -290 kJ • D) -1720 kJ

37. Ex. Combustion of MethaneCH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)

38. Hrxn° = [1Hf(c) + 2Hf(d)] -[1Hf(a) + 2Hf(b)] - Hrxn°= [-394kJ+(-572kJ)]-[-75kJ+0kJ]= -891kJ

39. QUESTION

40. Exo- and Endo- thermic(Exergonic and Endergonic) • Heat exchange accompanies chemical reactions. • Exothermic: Heat flows outof the system (to the surroundings).…negative sign • Endothermic: Heat flows intothe system (from the surroundings).…positive sign

41. QUESTION

42. Remember from earlier slides: http://chemconnections.org/general/chem120/Flash/specific_heat_s.swf (Cp) of a body: In obese mice (fat content 52.76% body wt) the heat capacity was 2.65 kJ kg-1 K-1 and in lean mice (fat content 7.55% body wt) the heat capacity was 3.66 kJ kg-1 K-1.

43. http://chemconnections.org/general/chem120/Flash/heat_transfer_s.swfhttp://chemconnections.org/general/chem120/Flash/heat_transfer_s.swf How does the relative (Cp) of the body of an obese person compared to that of a lean person relate to their relative rise in body temperatures if both persons exercise at exactly the same level?

44. “Heat of Reaction” Change in Enthalpy • The heat of any reaction can be calculated from enthalpies of formation of reactants and products.(“Hess’s Law”) Hrxn° = npHf(products) nrHf(reactants) http://chemconnections.org/general/chem120/Flash/hess_law_s.swf

45. Thermochemistry Lab Neutralization Reactions / Hess’s law HCl(aq) +NaOH(aq)NaCl(aq) + H2O(l) HNO3(aq) +NaOH(aq)NaNO3(aq) + H2O(l) NaOH(s) + H2O(l)NaOH(aq) HCl(aq) +NaOH(s)NaCl(aq) + H2O(l)

46. Calorimetry (Interactive)

47. Thermochemistry Lab Neutralization Reactions / Hess’s law Tfinal Tinitial

48. QUESTION

49. Report Table Results/Conclusions: answer questions #3,4,& 6 pg. 41 (DVC Lab Manual)

50. QUESTION