1. Thermodynamics (OWLBook Chapter 5) OWLBook Deadline 10/29/12

2. 5.1 Energy and Work

4. Kinetic Energy, E K The energy associated with an object by virtue of its motion. m = mass (kg) v = velocity (m/s) Potential Energy, E P The energy an object has by virtue of its position in a field of force, such as gravitaitonal, electric or magnetic field. Gravitational potential energy is given by the equation m = mass (kg) g = gravitational constant (9.80 m/s 2 ) h = height (m)

5. Units/Conversions/Conservat ion Law of Conservation of Energy Energy may be converted from one form to another, but the total quantity of energy remains constant.

6. Thermodynamic System The substance under study in which a change occurs is called the thermodynamic system (or just system). Thermodynamic Surroundings Everything else in the vicinity is called the thermodynamic surroundings (or just the surroundings).

7. Signs and Conventions

8. Enthalpy ( H ) Enthalpy, H An extensive property of a substance that can be used to obtain the heat absorbed or evolved in a chemical reaction. Extensive Property: A property that depends on the amount of substance. Mass and volume are extensive properties.

9. Endothermic or Exothermic

11. Let’s do quick the OWLBook Check 5.2.1

13. Applying Stoichiometry to Heats of Reaction

14. Enthalpy Change and Stoichiometry Sulfur, S 8, burns in air to produce sulfur dioxide. The reaction evolves 9.31 kJ of heat per gram of sulfur (S 8 ) at constant pressure. o Write the balanced chemical equation o Write a thermochemical equation for this reaction, expressing the change in enthalpy in kJ/mole of S 8. o If 48 grams of sulfur is burned in an excess of oxygen, how much heat is produced?

15. A bomb calorimeter

16. Energy and State Changes

17. Let’s do this and create the phase change diagram for this problem.

18. Enthalpy and Reactions Constant Pressure!

19. Remember Energy is Conserved 0 = q system + q surroundings q surroundings = (mass of calorimeter contents) x (specific heat) x ΔT ΔH = q system = -q surroundings

20. Specific Heat Capacity, s (or specific heat) o The quantity of heat needed to raise the temperature of one gram of substance by one degree Celsius (or one Kelvin) at constant pressure.

22. A piece of zinc weighing 35.8 g was heated from 20.00°C to 28.00°C. How much heat was required? The specific heat of zinc is 0.388 J/(g°C).

23. Let’s do OWLBook Tutorial 5.4.3.

24. Hess’s Law Enthalpy is a State Function. It is the starting point and ending point that matter, NOT how you get there.

25. Hess’s Law If you flip a reaction, the sign on ΔH changes. If you multiply a reaction by a number, ΔH gets multiplied by that same number. You can use any number or combination of reactions to get from point “A”-reactants to point “B” –products. Used when reactions are slow, hard to measure, or even theoretical (never been done before).

26. Suppose we want DH for the reaction 2C(graphite) + O 2 (g)  2CO(g) It is difficult to measure directly. However, two other reactions are known: 2CO 2 (g)  2CO(g) + O 2 (g); ΔH = – 566.0 kJ C(graphite) + O 2 (g)  CO 2 (g); ΔH = -393.5 kJ In order for these to add to give the reaction we want, we must multiply the first reaction by 2. Note that we also multiply ΔH by 2.

27. Copyright © Cengage Learning. All rights reserved. 6 | 27 Our Goal = 2C(graphite) + O 2 (g)  2CO(g) 2C(graphite) + 2O 2 (g)  2CO 2 (g);  H = -787.0 kJ 2CO 2 (g)  2CO(g) + O 2 (g);  H = – 566.0 kJ 2 C(graphite) + O 2 (g)  2 CO(g);  H = –1353.0 kJ

29. Copyright © Cengage Learning. All rights reserved. 6 | 29 What is the enthalpy of reaction,  H, for the reaction of calcium metal with water? Ca(s) + 2H 2 O(l)  Ca 2+ (aq) + 2OH - (aq) + H 2 (g) This reaction occurs very slowly, so it is impractical to measure  H directly. However, the following facts are known: H + (aq) + OH - (aq)  H 2 O(l);  H = –55.9 kJ Ca(s) + 2H + (aq)  Ca 2+ (aq) + H 2 (g);  H = –543.0 kJ

30. Standard Enthalpy Standard Enthalpies of Formation The term standard state refers to the standard thermodynamic conditions chosen for substances when listing or comparing thermodynamic data: o 1 atm pressure and the specified temperature (usually 25°C). o These standard conditions are indicated with a degree sign (°). When reactants in their standard states yield products in their standard states, the enthalpy of reaction is called the standard enthalpy of reaction,  H°. (  H° is read “ delta H zero. ” )

31. The standard enthalpy of formation,  H f °, is the enthalpy change for the formation of one mole of the substance from its elements in their reference forms and in their standard states.  H f ° for an element in its reference and standard state is zero. For example, the standard enthalpy of formation for liquid water is the enthalpy change for the reaction H 2 (g) + 1 / 2 O 2 (g)  H 2 O(l)  H f ° = –285.8 kJ Other  H f ° values are found in various reference tables (not necessary to be memorized, except for…  H f ° for an element in its reference and standard state

32. Remember, these are for formation of these substances from their constituent elements in reference states.

33. Using Standard Enthalpies of Formation…. We want  H° for the reaction: CH 3 OH(l)  CH 3 OH(g)  H vap = +38.0 kJ

34. Methyl alcohol, CH 3 OH, is toxic because liver enzymes oxidize it to formaldehyde, HCHO, which can coagulate protein. Calculate  H o for the following reaction: 2CH 3 OH(aq) + O 2 (g)  2HCHO(aq) + 2H 2 O(l) Standard enthalpies of formation, : CH 3 OH(aq):-245.9 kJ/mol HCHO(aq):-150.2 kJ/mol H 2 O(l):-285.8 kJ/mol