1. Thermochemistry Chapters 6 and11

2. TWO Trends in Nature ___________  _________  _____ energy  ____ energy 

3. _________ is any process that gives off heat – transfers thermal energy from the ______ to the _________. __________ is any process in which heat has to be supplied to the _______ from the _________ 2H 2 (g) + O 2 (g) 2H 2 O (l) + energy H 2 O (g) H 2 O (l) + energy energy + 2HgO (s) 2Hg (l) + O 2 (g) 6.2 energy + H 2 O (s) H 2 O (l)

4. _________ is used to quantify the heat flow into or out of a system in a process that occurs at constant ________.  H = H (________) – H (________)  H = heat given off or absorbed during a reaction at constant pressure  H < 0  H > 0 6.4

5. Thermochemical Equations H 2 O (s) H 2 O (l)  H = 6.01 kJ Is  H negative or positive? System ______ heat _____thermic  H ____ 0 6.01 kJ are _______ for every 1 mole of ice that _____at 0 0 C and 1 atm. 6.4

6. Thermochemical Equations CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O (l)  H = -890.4 kJ Is  H negative or positive? System gives off heat ______thermic  H____ 0 890.4 kJ are ________for every 1 mole of methane that is combusted at 25 0 C and 1 atm. 6.4

7. H 2 O (s) H 2 O (l)  H = 6.01 kJ/mol ΔH = 6.01 kJ The ______________________always refer to the number of moles of a substance Thermochemical Equations If you reverse a reaction, the ______ of  H changes H 2 O (l) H 2 O (s)  H = - 6.01 kJ If you multiply both sides of the equation by a factor n, then  H must change by the same factor n. 2H 2 O (s) 2H 2 O (l)  H = 2 mol x 6.01 kJ/mol = 12.0 kJ 6.4

8. H 2 O (s) H 2 O (l)  H = 6.01 kJ The ___________of all reactants and products must be specified in thermochemical equations. Thermochemical Equations 6.4 H 2 O (l) H 2 O (g)  H = 44.0 kJ How much heat is evolved when 266 g of white phosphorus (P 4 ) burn in air? P 4 (s) + 5O 2 (g) P 4 O 10 (s)  H reaction = -3013 kJ

9. _________________  H 0 ) is the heat change that results when ________ of a compound is formed from its _______ at a pressure of 1 atm. f The standard enthalpy of formation of any element in its most stable form is ______.  H 0 (O 2 ) = 0 f  H 0 (O 3 ) = 142 kJ/mol f  H 0 (C, graphite) = 0 f  H 0 (C, diamond) = 1.90 kJ/mol f 6.6

11. The ________________(  H 0 ) is the enthalpy of a reaction carried out at 1 atm. rxn aA + bB cC + dD H0H0 rxn d  H 0 (D) f c  H 0 (C) f = [+] - b  H 0 (B) f a  H 0 (A) f [+] H0H0 rxn  H 0 (________) f =  f  - 6.6 Hess’s Law: ?????? (Enthalpy is a _________ function. It doesn’t matter how you get there, only where you start and end.)

12. Benzene (C 6 H 6 ) burns in air to produce carbon dioxide and liquid water. How much heat is released per mole of benzene combusted? The standard enthalpy of formation of benzene is 49.04 kJ/mol. 2C 6 H 6 (l) + 15O 2 (g) 12CO 2 (g) + 6H 2 O (l) H0H0 rxn  H 0 (products) f =   H 0 (reactants) f  - 6.6

13. Calculate the standard enthalpy of formation of CS 2 (l) given that: C (graphite) + O 2 (g) CO 2 (g)  H 0 = -393.5 kJ rxn S (rhombic) + O 2 (g) SO 2 (g)  H 0 = -296.1 kJ rxn CS 2 (l) + 3O 2 (g) CO 2 (g) + 2SO 2 (g)  H 0 = -1072 kJ rxn 1. Write the enthalpy of formation reaction for CS 2 C (graphite) + 2S (rhombic) CS 2 (l) 2. Add the given rxns so that the result is the desired rxn. 6.6

14. Chemistry in Action: Fuel Values of Foods and Other Substances C 6 H 12 O 6 (s) + 6O 2 (g) 6CO 2 (g) + 6H 2 O (l)  H = -2801 kJ/mol 1 cal = 4.184 J 1 Cal = 1000 cal = 4184 J

15. The __________________-is the heat generated or absorbed when a certain amount of solute dissolves in a certain amount of solvent. 6.7 Which substance(s) could be used for melting ice? Which substance(s) could be used for a cold pack?

16. The Solution Process for NaCl  H soln = Step 1 + Step 2 = 788 – 784 = 4 kJ/mol 6.7

17. Energy Diagrams ExothermicEndothermic (a)Activation energy (Ea) for the forward reaction (b)Activation energy (Ea) for the reverse reaction (c) Delta H 50 kJ/mol300 kJ/mol 150 kJ/mol100 kJ/mol -100 kJ/mol+200 kJ/mol

18. ________________is a measure of the ________________ _______________of a system. orderS disorder S If the change from initial to final results in an increase in randomness  S ____ 0 For any substance, the solid state is more ordered than the liquid state and the liquid state is more ordered than gas state S _______ < S l________ << S _____ H 2 O (s) H 2 O (l)  S ____ 0 18.3

19. ______ Law of Thermodynamics Energy _________ converted from one form to another but energy ___________ be created or destroyed. ______Law of Thermodynamics The entropy of the ______increases in a ________process and remains unchanged in an _________ process.  S univ =  S sys +  S surr ____ 0 ___________ process:  S univ =  S sys +  s surr _____ 0 ___________ process: 18.4

20. Entropy Changes in the System (  S sys ) aA + bB cC + dD S0S0 rxn dS 0 (D) cS 0 (C) = [+] - bS 0 (B) aS 0 (A) [+] S0S0 rxn S 0 ()________) =  S 0 (________)  - The ________________ (  S 0 ) is the entropy change for a reaction carried out at 1 atm and 25 0 C. rxn 18.4 What is the standard entropy change for the following reaction at 25 0 C? 2CO (g) + O 2 (g) 2CO 2 (g) S 0 (CO) = 197.9 J/K mol S 0 (O 2 ) = 205.0 J/K mol S 0 (CO 2 ) = 213.6 J/K mol S0S0 rxn S0S0 l

21. Entropy Changes in the System (  S sys ) 18.4 When gases are produced (or consumed) If a reaction produces more gas molecules than it consumes,  S 0 ____ 0. If the total number of gas molecules diminishes,  S 0 ____ 0. If there is no net change in the total number of gas molecules, then  S 0 may be _______________BUT  S 0 will be a _____ number. What is the sign of the entropy change for the following reaction? 2Zn (s) + O 2 (g) 2ZnO (s)

22. _______________ Physical and Chemical Processes A waterfall runs ________ A lump of sugar ________ in a cup of coffee Heat flows _____ a hotter object ____ a colder object A gas _______ in an evacuated bulb Iron exposed to oxygen and water forms ___ spontaneous nonspontaneous 18.2

23.  S univ =  S sys +  S surr ___ 0 Spontaneous process:  S univ =  S sys +  S surr ____ 0 Equilibrium process: Gibbs Free Energy For a constant-temperature process:  G =  H sys -T  S sys Gibbs free energy (G)  G __ 0 The reaction is ________ in the forward direction.  G __ 0 The reaction is ________ as written. The reaction is _______ in the _______direction.  G ___ 0 The reaction is at ______. 18.5

24.  G =  H - T  S 18.5

25. aA + bB cC + dD G0G0 rxn d  G 0 (D) f c  G 0 (C) f = [+] - b  G 0 (B) f a  G 0 (A) f [+] G0G0 rxn  G 0 (_______) f =   G 0 (_______________) f  - The __________________ (  G 0 ) is the free-energy change for a reaction when it occurs under ________ conditions. _______________(  G 0 ) is the free-energy change that occurs when ______ of the compound is formed from its elements in their standard states. f  G 0 of any element in its stable form is __________. f

26. 2C 6 H 6 (l) + 15O 2 (g) 12CO 2 (g) + 6H 2 O (l) G0G0 rxn  G 0 (products) f =   G 0 (reactants) f  - What is the standard free-energy change for the following reaction at 25 0 C? G0G0 rxn = Is the reaction spontaneous at 25 0 C? 18.5

27. Recap: Signs of Thermodynamic Values NegativePositive Enthalpy (ΔH) Entropy (ΔS) Gibbs Free Energy (ΔG)

28. Gibbs Free Energy and Chemical Equilibrium  G =  G 0 + RT lnQ R is the gas constant (8.314 J/K mol) T is the absolute temperature (K) Q is the reaction quotient At Equilibrium 18.6

29.  G 0 =  RT lnK 18.6

30. The __________[most books use lower case c] of a substance is the amount of heat (q) required to raise the temperature of ________of the substance by ______ Celsius. The ________of a substance is the amount of heat (q) required to raise the temperature of ___________ (m) of the substance by ______ Celsius. Heat (q) absorbed or released: 6.5

31. How much heat is given off when an 869 g iron bar cools from 94 0 C to 5 0 C? 6.5

32. Constant-Pressure Calorimetry No heat enters or leaves! 6.5

34. The _____________is the temperature at which the (equilibrium) ______________of a liquid is equal to the __________pressure. The _______________ is the temperature at which a liquid boils when the _______________ pressure is ____atm. 11.8 Phase Changes

35. The _______________ is the temperature above which the gas cannot be made to _______, no matter how great the applied pressure. The __________ (P c ) is the minimum pressure that must be applied to bring about _______ at the critical temperature. 11.8

36. Where’s Waldo? Can you find… The Triple Point? Critical pressure? Critical temperature? Where fusion occurs? Where vaporization occurs? Melting point (at 1 atm)? Boiling point (at 6 atm)? Carbon Dioxide

37. 11.8 H 2 O (s) H 2 O (l) The melting point of a solid or the freezing point of a liquid is the temperature at which the _____ and _____ phases coexist in ______

38. 11.8 H 2 O (s) H 2 O (g) Molar heat ________(  H sub ) is the energy required to sublime 1 mole of a solid. ( Hess’s Law)

39. Molar heat of fusion (  H fus ) is the energy required to melt 1 mole of a solid substance. 11.8

41. Sample Problem How much heat is required to change 36 g of H 2 O from -8 deg C to 120 deg C?

42. Sample Problem How much heat is required to change 36 g of H 2 O from -8 deg C to 120 deg C?