1. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Energy The capacity to do work or to produce heat.

2. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Law of Conservation of Energy Energy can be converted from one form to another but can neither be created nor destroyed. (E universe is constant)

3. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 The Two Types of Energy Potential: due to position or composition - can be converted to work Kinetic: due to motion of the object KE = 1 / 2 mv 2 (m = mass, v = velocity)

4. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Temperature v. Heat See fig 6.1, p. 242. Note changes in KE/PE Why does B not get as high as A? Frictional heating: hill gets hotter Temperature reflects random motions of particles, therefore related to kinetic energy of the system. Heat involves a transfer of energy between 2 objects due to a temperature difference

5. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Work In fig 6.1, B gains PE because work was done on B by A. Work: f x d. So, energy can be transferred two ways: through work and through heat. For ball A, PE lost as work or heat depends on pathway.

6. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 State Function Depends only on the present state of the system - not how it arrived there. It is independent of pathway.

7. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 A note about state functions Would you agree that the distance between Chicago and L.A. is fixed? This “fixed distance” is analogous to a State Function. But the pathway, how we get to L.A. from Chicago, is not fixed. Energy is a state function Work and Heat are not state functions

8. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 System and Surroundings System: That on which we focus attention Surroundings: Everything else in the universe Universe = System + Surroundings

9. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 System/Surroundings Example: CH 4 + O 2 --> CO 2 + 2H 2 O + heat System: the reaction inside your furnace Surroundings: everything else (furnace, house, everything else

10. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Exo and Endothermic Heat exchange accompanies chemical reactions. Exothermic: Heat flows out of the system (to the surroundings). Endothermic: Heat flows into the system (from the surroundings). Where does the the heat come from? Fig 6.2/6.3 pg 244

11. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Figure 6.2 The Combustion of Methane

12. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Figure 6.3: The Energy Diagram for the Reaction of Nitrogen and Oxygen to Form Nitric Oxide

13. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 First Law First Law of Thermodynamics: The energy of the universe is constant.

14. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 First Law  E = q + w  E = change in system’s internal energy q = heat w = work

15. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Signs We always take they systems p.o.v. q= + for endothermic ( energy flows into the system q = - for exo, (energy flows out system) w = - (system does work on surr) w = + (surr do work on the system)

16. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Figure 6.4 The Volume of a Cylinder

17. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 PV Work (look at fig 6.4 page 246) work = force  distance, force x  h since P = force / area, (force = P x area) work = (pressure x area) x  h w =  P  V expanding gas: work is neg, work done on surr compressed gas: work is pos (  V is neg), work done on sys

18. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Enthalpy Enthalpy = H = E + PV  E =  H  P  V  H =  E + P  V At constant pressure,  E = q P  P  V or q P =  E + P  V, where q P =  H at constant pressure  H = energy flow as heat (at constant pressure)

19. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 Change in Enthalpy Flow of heat is change in ethalpy  H = H products  H reactants  H = neg exothermic  H = pos endothermic

20. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 Calorimetry Science of measuring heat. Calorimeter --> Heat capacity: energy required to change the temperature of a substance. C = heat absorbed (Joules) Increase in temp

21. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Figure 6.6 A Bomb Calorimeter

22. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 Heat Capacity

23. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 Heat Exchange Terms specific heat capacity heat capacity per gram = J/°C g or J/K g ex. Water: 4.18 J/ °C g molar heat capacity heat capacity per mole = J/°C mol or J/K mol

24. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24 Hess’s Law Reactants  Products The change in enthalpy is the same whether the reaction takes place in one step or a series of steps.

25. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 Figure 6.7 The Principle of Hess’s Law

26. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 26 Calculations via Hess’s Law 1. If a reaction is reversed,  H is also reversed. N 2 (g) + O 2 (g)  2NO(g)  H = 180 kJ 2NO(g)  N 2 (g) + O 2 (g)  H =  180 kJ 2. If the coefficients of a reaction are multiplied by an integer,  H is multiplied by that same integer. 6NO(g)  3N 2 (g) + 3O 2 (g)  H =  540 kJ

27. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 27 Standard States Compound 4 For a gas, pressure is exactly 1 atmosphere. 4 For a solution, concentration is exactly 1 molar. 4 Pure substance (liquid or solid), it is the pure liquid or solid. Element 4 The form [N 2 (g), K(s)] in which it exists at 1 atm and 25°C.

28. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 28 Change in Enthalpy Can be calculated from enthalpies of formation of reactants and products.  H rxn ° =  n p  H f  (products)   n r  H f  (reactants)

29. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 29 Figure 6.10 A Pathway for the Combustion of Ammonia

30. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 30 Figure 6.11 Energy Sources Used in the United States

31. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 31 Petroleum/nat. gas From marine organisms 500 my ago Petroleum: liquid mix of hydrocarbons Natural Gas: methane, ethane, butane, propane. Petroleum separated by separated by boiling point. Table 6.3/6.4 Kerosene the original: replacewhale oil/animal fats in oil lamps

32. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 32 Fractional Distillation

33. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 33 Coal From plants, dead, buried with heat/pressure. ( 300 my ago) Cellulose (CH 2 O empirical) from plants slowly becomes more pure in C. 300 my ago nothing evolved yet to eat cellulose. Use expected to increase - problems

34. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 34 Figure 6.12 The Earth’s Atmosphere

35. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 35 Figure 6.13 Atmospheric CO 2 Concentration

36. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 36 What other energy sources do we have? Coal gasification:syngas AK could benefit Hydrogen. Oil shale Nuclear

37. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 37 Figur e 6.14 Coal Gasifi cation

38. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 38 Hydrogen H 2 +.5O 2 --> H 2 O ∆H ˚ = -286 kJ Much greater than methane Problems: production, storage, transport Production: a. CH 4 + H 2 O --> 3 H 2 + CO ∆H ˚ = 206 kJ ( b. Decomp water ∆H ˚ = 286 kJ