1. 1 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Section 18 Thermodynamics and Entropy

2. 2 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Thermochemistry Thermodynamics is the science of the relationship between heat and other forms of energy. Thermochemistry is the study of the quantity of heat absorbed or evolved (released) by chemical reactions. Why do chemical reactions occur? What is the driving force of rxn? Answer: Stability, wants to get to lower E. For a rxn to take place spontaneously the products of reaction must be more stable (lower E) than the starting reactants. Nonspontaneous means never happen by self.

3. 3 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Heat of Reaction In chemical reactions, heat is often transferred from the “system or reaction” to its “surroundings,” or vice versa. system - the substance or mixture of substances under study in which a change occurs. The surroundings are everything in the vicinity of the thermodynamic system.

4. 4 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Heat of Reaction Heat is defined as the energy that flows into or out of a system. We follow heat by watching the difference in temperature between the system and its surroundings. Often we follow the surroundings temp (solvent) and must realize that the opposite is happening to the system. If system is absorbing heat from the surroundings than the temp of the surroundings must be decreasing.

5. 5 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Heat of Reaction Heat is denoted by the symbol q.  For an endothermic rxn the sign of q is positive; heat is absorbed by the system from the surroundings.  For an exothermic rxn, the sign of q is negative if heat is evolved (released) by the system to the surroundings. –Heat of Reaction is the value of q required to return a system to the given temperature at the completion of the reaction.

6. 6 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Heat of Reaction Exothermicity  “out of” a system  q < 0 Endothermicity  “into” a system  q > 0 Energy System Surroundings Energy System Surroundings

7. 7 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Enthalpy and Enthalpy Change The heat absorbed or evolved by a reaction depends on the conditions under which it occurs. ex. pressure Usually, a reaction takes place in an open vessel, and therefore under the constant pressure of the atmosphere. heat of this type of reaction is denoted q p, the heat at constant pressure named enthalpy and given symbol H. H is the heat content at constant pressure.

8. 8 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –an extensive property - depends on the quantity of substance. –Enthalpy is a state function, a property of a system that depends only on its present state and is independent of any previous history of the system. Enthalpy and Enthalpy Change Enthalpy, denoted H, is an extensive property of a substance that can be used to obtain the heat absorbed or evolved in a chemical reaction at constant pressure.

9. 9 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. The change in enthalpy for a reaction at a given temperature and pressure Enthalpy and Enthalpy Change

10. 10 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. As we already stated the change in enthalpy is equal to the heat of reaction at constant pressure. This represents the entire change in internal energy (  U) minus any expansion “work” done by the system; therefore we can define enthalpy and internal work by the 1st law of thermodynamics: In any process, the total change in energy of the system,  U, is equal to the sum of the heat absorbed, q, and the work, w, done by the system.  U = q p + w =  H + w Enthalpy and Enthalpy Change

11. 11 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –Changes in E manifest themselves as exchanges of energy between the system and surroundings. –These exchanges of energy are of two kinds; heat and work - must account for both. –Heat is energy that moves into or out of a system because of a temperature difference between system and surroundings. –Work is the energy exchange that results when a force F moves an object through a distance d; work (w) = F  d In chemical systems, work is defined as a change in volume at a given pressure, that is:

12. 12 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. negative sign is to keep sign correct in terms of system. For expansion,  V, will be a positive value but expansion involves the system doing work on the surroundings and a decrease in internal energy -- negative keeps it neg. For contraction work,  V, will be a negative value but contraction involves the surroundings doing work on the system and an increase in internal energy -- negative keeps it positive (- x - = +). Giving us the 1st law of thermo is more useful form: realize absorb heat (+) release or evolved heat (-) HW 44

13. 13 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Thermochemical Equations A thermochemical equation is the chemical equation for a reaction (including phase labels {important}) in which the equation is given a molar interpretation, and the enthalpy of reaction for these molar amounts is written directly after the equation. If  H has a superscript like  H o, means thermo standard conditions -- 25 o C (298K) and 1 atm.

14. 14 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. The following are two important rules for manipulating thermochemical equations: –1.) When a thermochemical equation is multiplied by any factor, the value of  H for the new equation is obtained by multiplying the  H in the original equation by that same factor. –2.) When a chemical equation is reversed, the value of  H is reversed in sign. Thermochemical Equations exo endo

15. 15 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Hess’s law of heat summation states that for a chemical equation that can be written as the sum of two or more steps, the enthalpy change for the overall equation is the sum of the enthalpy changes for the individual steps. Basically, R & P in individual steps can be added like algebraic quantities in determining overall equation and enthalpy change. Hess’s Law

16. 16 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. simple example : Given: A + D  B  H = X kJ A + B  C  H = Y kJ Question: 2C + 2D  4B  H = ?

17. 17 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. For example, suppose you are given the following GIVEN data: Hess’s Law use these data to obtain the enthalpy change for the following reaction?

18. 18 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. If we multiply the first equation by 2 and reverse the second equation, they will sum together to become the third. HW 45

19. 19 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. The standard enthalpy of formation of a substance, denoted  H f o, is the enthalpy change for the formation of one mole of a substance in its standard state from its component elements in their standard state (298K & 1 atm). –Note that the standard enthalpy of formation for a pure element in its standard state and H + is zero. This means elements in their standard state has  H f o = 0: metals - solids, diatomic gases, H + ion. Standard Enthalpies of Formation (molecular scale)

20. 20 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Another way to determine heat of reaction is the The law of summation of heats of formation which states that the enthalpy of a reaction is equal to the total formation energy of the products minus that of the reactants..  is the mathematical symbol meaning “the sum of”, and m and n are the coefficients of the substances in the chemical equation. Standard Enthalpies of Formation

21. 21 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Ex. Generic Law of Summation aA + bB  cC + dD

22. 22 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. A Problem to Consider –What is the standard enthalpy change for this reaction?

23. 23 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Using the summation law: –Be careful of arithmetic signs as they are a likely source of mistakes. HW 46

24. 24 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –Entropy, S, is a thermodynamic quantity that is a measure of the randomness or disorder of a system. –The SI unit of entropy is joules per Kelvin (J/K) and, like enthalpy, is a state function. Entropy and the Second Law of Thermodynamics The second law of thermodynamics addresses questions about spontaneity in terms of a quantity called entropy.

25. 25 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline.

26. 26 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. entropy (S) - is a thermodynamic quantity that is a measure of how dispersed the energy of a system is among the different possible ways that system can contain energy, typically in J/K units. One example of entropy is the amount of molecular disorder or randomness in the system. S increases as disorder increases and energy decreases gases have high disorder, low energy solids have low disorder, high energy We typically follow the change in entropy in the system so we treat it as a state property and measure  S = S final - S initial +  S = increase in entropy, i.e. disorder increased -  S = decrease in entropy, ie. disorder decreased This gets us to the second law of thermo

27. 27 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Entropy and the Second Law of Thermodynamics The second law of thermodynamics states that the total entropy of a system and its surroundings increases for a spontaneous process.

28. 28 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. The tendency of a system to increase its entropy (+  S) is the second important factor in determining the spontaneity of a chemical or physical change in addition to  H. recap: spontaneous process: (system goes to lower energy state) favored by -  H (exo) favored by +  S (ie. increase disorder) nonspontaneous process: (system goes to higher energy state) favored by +  H (endo) favored by -  S (ie. decrease in disorder) Do both need to be true for spon rxn? No, remember soluble salt dissolving example. The larger term will dictate overall process.

29. 29 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –As temperature is raised the substance becomes more disordered as it absorbs heat and becomes a liquid then a gas, where entropy > 0; S increases as temp increase. –The entropy of a substance is determined by measuring how much heat is required to change its temperature per Kelvin degree (J/K). Standard Entropies and the Third Law of Thermodynamics The third law of thermodynamics states that a substance that is perfectly crystalline at 0 K has an entropy of zero.

30. 30 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –Standard state implies 25 o C (298K), 1 atm pressure, and 1 M for dissolved substances.(Thermo standard state) Standard Entropies and the Third Law of Thermodynamics The standard entropy of a substance or ion, also called its absolute entropy, S o, is the entropy value for the standard state of the species. Similar to heats of formation,  H f o, except on absolute not relative scale.

31. 31 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –This means that elements have nonzero values for entropy (absolute scale), unlike standard enthalpies of formation,  H f o, which by convention, are zero (relative scale). Standard Entropies and the Third Law of Thermodynamics –The symbol S o, rather than  S o, is used for standard entropies to emphasize that they originate from the third law and absolute not relative values.

32. 32 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –Even without knowing the values for the entropies of substances, you can sometimes predict the sign of  S o for a reaction. Entropy Change for a Reaction You can calculate the entropy change for a reaction using a summation law, similar to the way you obtained  H f o.

33. 33 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. 1.A reaction in which a molecule is broken into two or more smaller molecules. The entropy usually increases in the following situations: Entropy Change for a Reaction 2.A reaction in which there is an increase in the moles of gases. 3.A process in which a solid changes to liquid or gas or a liquid changes to gas.

34. 34 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Predict  S and spon/nonspon based only on entropy for the following rxns: C 2 H 4 (g) + Br 2 (g) --> BrCH 2 CH 2 Br (l) 2 C 2 H 6 (g) + 7 O 2 (g) --> 4 CO 2 (g) + 6 H 2 O (g) C 6 H 12 O 6 (s) --> 2 C 2 H 5 OH (l) + 2 CO 2 (g) HW 47

35. 35 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –The calculation is similar to that used to obtain  H o from standard enthalpies of formation. A Problem To Consider Calculate the change in entropy,  S o, at 25 o C for the reaction in which urea is formed from NH 3 and CO 2.

36. 36 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. So:So:193 J/mol. K21417470 A Problem To Consider

37. 37 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –This quantity gives a direct criterion for spontaneity of reaction. Free Energy Concept The question arises as to how do we decide if enthalpy or entropy dictates the spontaneity of a reaction. What is the relationship between  H and  S? The American physicist J. Willard Gibbs introduced the concept of free energy (sometimes called the Gibbs free energy), G, which is a thermodynamic quantity defined by the equation   G=  H-T  S

38. 38 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. At a given temperature and pressure  G = 0, the reaction gives an equilibrium mixture with significant amounts of both reactants and products (transfer point where reaction switches spon/nonspon)  G > 0, the reaction is nonspontaneous as written, and reactants do not give significant amounts of product at equilibrium.  G < 0, the reaction is spontaneous as written, and the reactants transform almost entirely to products when equilibrium is reached. Free Energy and Spontaneity Changes in H an S during a reaction result in a change in free energy,  G, given by the equation

39. 39 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. HH SS GG Description – spon+spon–sponSpontaneous at all T +non–non+nonNonspontaneous at all T –spon–non+ or – Spontaneous at low T (room); Nonspontaneous at high T (1000K) +non+spon+ or – Nonspontaneous at low T; Spontaneous at high T Spontaneity and Temperature Change Lets look at relationship among the signs of  H,  S and  G and spontaneity. Note that temperature will dictate which will rule. Also realize T is in K meaning no negative temp. enthalpy rules at low temp but entropy at very high T

40. 40 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –The next example illustrates the calculation of the standard free energy change,  G o, from  H o and  S o. Standard Free-Energy Change The standard free energy change,  G o, is the free energy change that occurs when reactants and products are in their standard states.

41. 41 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. So:So: 130.6191.5193 J/mol K Hfo:Hfo: 00-45.9 kJ/mol A Problem To Consider What is the standard free energy change,  G o, for the following reaction at 25 o C?

42. 42 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –Now substitute into our equation for  G o. Note that  S o is converted to kJ/K and Kelvin for temp. spon rxn as written So:So: 130.6191.5193 J/mol K Hfo:Hfo: 00-45.9 kJ/mol

43. 43 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –By tabulating  G f o for substances, you can calculate the  G o for a reaction by using a summation law. Standard Free Energies of Formation The standard free energy of formation,  G f o, of a substance is the free energy change that occurs when 1 mol of a substance is formed from its elements in their stablest states at 1 atm pressure and 25 o C.

44. 44 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. Gfo:Gfo: -174.80-394.4-228.6 kJ/mol A Problem To Consider Calculate  G o for the following reaction at 25 o C using std. free energies of formation.

45. 45 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –Here Q is the thermodynamic form of the reaction quotient ([products]/[reactants] not necessarily at equil). Relating  G o to the Equilibrium Constant The free energy change (  G) when reactants are in non-standard states (meaning other than 1 atm pressure or 1 M) is related to the standard free energy change,  G o, by the following equation.

46. 46 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –  G represents an instantaneous change in free energy at some point in the reaction approaching equilibrium  G=0. Relating  G o to the Equilibrium Constant –At equilibrium,  G=0 and the reaction quotient Q becomes the equilibrium constant K.

47. 47 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –When K > 1 (meaning equil lies to the right), the ln K is positive and  G o is negative (spon). –When K < 1 (meaning equil lies to the left), the ln K is negative and  G o is positive (nonspon). This result easily rearranges to give the basic equation relating the standard free-energy change to the equilibrium constant. Relating  G o to the Equilibrium Constant

48. 48 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –Rearrange the equation  G o = -RTlnK to give A Problem To Consider Find the value for the equilibrium constant, K, at 25 o C (298 K) for the following reaction. The standard free-energy change,  G o, at 25 o C equals –13.6 kJ/mol.

49. 49 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –Substituting numerical values into the equation, A Problem To Consider

50. 50 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –You get the value of  G T o at any temperature T by substituting values of  H o and  S o at 25 o C into the following equation. Calculation of  G o at Various Temperatures We typically assume that  H o and  S o are essentially constant with respect to temperature.

51. 51 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. So:So: 38.292.9213.7 J/mol K Hfo:Hfo: -635.1-1206.9-393.5 kJ/mol A Problem To Consider Find the  G o for the following reaction at 25 o C and 1000 o C. Relate this to reaction spontaneity.

52. 52 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –Now you substitute  H o,  S o (=0.1590 kJ/K), and T (=298K) into the equation for  G f o. So the reaction is nonspontaneous at 25 o C. So:So: 38.292.9213.7 J/mol K Hfo:Hfo: -635.1-1206.9-393.5 kJ/mol

53. 53 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. A Problem To Consider Find the  G o for the following reaction at 1000 o C. –Now we’ll use 1000 o C (1273 K) along with our previous values for  H o and  S o because assume does not change much. So the reaction is spontaneous at 1000 o C. You see that this reaction change from nonspon to spon somewhere between 25 o C to 1000 o C. How can we determine at what temp this switch occurred?

54. 54 Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline. –To determine the minimal temperature for spontaneity, we can set  Gº=0 and solve for T. –Thus, CaCO 3 should be thermally stable until its heated to approximately 848 o C. –This is way you could calculate the normal boiling point of a liquid. At  G=0, the liquid phase and gas phase will be at equilibrium; temperature at which switch from liquid to gaseous phase. HW 48