1. The total heat gained by the calorimeter + water contents = 4.28 x 10 3 J + 6.89 x 10 3 J = 1.117 x 10 4 J So we can write the following equivalence statement: 0.569 g benzoic acid 1.117 x 10 4 J The molar mass of benzoic acid = 122 g/mol Therefore the amount of heat released when 1 mol of benzoic is burned is: 121

2. = 1 mol benzoic acid x = 2.39 x 10 3 kJ 122

3. = 1 mol benzoic acid x = 2.39 x 10 3 kJ In this case, since the volume is constant, we have actually determined the change in internal energy of benzoic acid to be -2.39 x 10 3 kJ/mol. 123

4. 124

5. 125

6. A short list of common “reaction” types Heat of “Reaction” Example 126

7. A short list of common “reaction” types Heat of “Reaction” Example Enthalpy of solution: NH 4 NO 3(s) NH 4 + (aq) + NO 3 - (aq) H 2 O 127

8. A short list of common “reaction” types Heat of “Reaction” Example Enthalpy of solution: NH 4 NO 3(s) NH 4 + (aq) + NO 3 - (aq) H 2 O Enthalpy of dilution: H 2 SO 4(aq) H 2 SO 4(aq) H 2 O 128

9. A short list of common “reaction” types Heat of “Reaction” Example Enthalpy of solution: NH 4 NO 3(s) NH 4 + (aq) + NO 3 - (aq) H 2 O Enthalpy of dilution: H 2 SO 4(aq) H 2 SO 4(aq) H 2 O Enthalpy of fusion: H 2 O (s) H 2 O (l) 129

10. A short list of common “reaction” types Heat of “Reaction” Example Enthalpy of solution: NH 4 NO 3(s) NH 4 + (aq) + NO 3 - (aq) H 2 O Enthalpy of dilution: H 2 SO 4(aq) H 2 SO 4(aq) H 2 O Enthalpy of fusion: H 2 O (s) H 2 O (l) Enthalpy of vaporization: H 2 O (l) H 2 O (g) 130

11. A short list of common “reaction” types Heat of “Reaction” Example Enthalpy of solution: NH 4 NO 3(s) NH 4 + (aq) + NO 3 - (aq) H 2 O Enthalpy of dilution: H 2 SO 4(aq) H 2 SO 4(aq) H 2 O Enthalpy of fusion: H 2 O (s) H 2 O (l) Enthalpy of vaporization: H 2 O (l) H 2 O (g) Enthalpy of reaction: MgCl 2(s) + 2 Na (s) 2 NaCl (s) + Mg (s) 131

12. Applications of thermochemistry 1. BB 2. SHSC 132

13. Chemical Kinetics 133

14. Chemical Kinetics: The study of rates and mechanisms of chemical reactions. 134

15. Chemical Kinetics: The study of rates and mechanisms of chemical reactions. The word rate means the change of a certain quantity with time. In the present case, it will be a change of concentration of a reactant or product with time that will be of interest. 135

16. Two Key Questions If a reaction goes, how fast? 136

17. Reaction Rate: A measure of how rapidly a reaction occurs. It is the change of a reactant or product concentration divided by the time interval required for the change to occur. 137

18. Reaction Rate: A measure of how rapidly a reaction occurs. It is the change of a reactant or product concentration divided by the time interval required for the change to occur. Reaction Mechanism: The sequence of elementary steps that lead to product formation. 138

19. Factors that affect the reaction rate. 139

20. Factors that affect the reaction rate. 1. Nature of the reactants: Elements and compounds in general, have differing reactivities. That is, different tendencies toward bond formation and bond breaking. 140

21. Factors that affect the reaction rate. 1. Nature of the reactants: Elements and compounds in general, have differing reactivities. That is, different tendencies toward bond formation and bond breaking. 2. The ability of the reactants to meet: The gas phase and liquid phase allow the possibility for reactants to intermingle on the molecular level. 141

22. Factors that affect the reaction rate. 1. Nature of the reactants: Elements and compounds in general, have differing reactivities. That is, different tendencies toward bond formation and bond breaking. 2. The ability of the reactants to meet: The gas phase and liquid phase allow the possibility for reactants to intermingle on the molecular level. The solid phase is generally a very poor medium for chemical reactions. 142

23. The effect of surface area on reaction rate. 143

24. If all the reactants are in the same phase (e.g. all in solution) the reaction is called a homogeneous reaction. 144

25. If all the reactants are in the same phase (e.g. all in solution) the reaction is called a homogeneous reaction. If all the reactants are not in the same phase (e.g. a gas reacting with a solid surface) the reaction is called a heterogeneous reaction. 145

26. If all the reactants are in the same phase (e.g. all in solution) the reaction is called a homogeneous reaction. If all the reactants are not in the same phase (e.g. a gas reacting with a solid surface) the reaction is called a heterogeneous reaction. Factors such as molecular shape have an extremely important bearing on whether reactive centers in different reactants can meet. 146

27. 3. The concentration of the reactants. This is obviously closely linked to number 2 above. 147

28. 3. The concentration of the reactants. This is obviously closely linked to number 2 above. 4. The temperature of the system. 148

29. 3. The concentration of the reactants. This is obviously closely linked to number 2 above. 4. The temperature of the system. 5. The presence of catalysts. 149

30. 3. The concentration of the reactants. This is obviously closely linked to number 2 above. 4. The temperature of the system. 5. The presence of catalysts. A catalyst is defined as follows: A substance that increases the rate of reaction without being used up. 150

31. Note: This definition of a catalyst does not exclude the possibility that the catalyst undergoes some chemistry. If it does in some step, it has to be regenerated in a sequent step in the overall reaction scheme. 151

32. Rate of Reaction The reaction rate is the change in concentration of a particular reactant or product. The unit of concentration most commonly employed is mol/liter, that is the molar concentration unit. Two common time units are seconds or minutes. 152

33. Rate of Reaction The reaction rate is the change in concentration of a particular reactant or product. The unit of concentration most commonly employed is mol/liter, that is the molar concentration unit. Two common time units are seconds or minutes. The most common unit of reaction rate is thus: (mol/liter)/second = mol l -1 s -1 = Ms -1 153

34. Consider the reaction: O CH 3 C Cl + H 2 O CH 3 CO 2 H + HCl acetyl chloride 154

35. Consider the reaction: O CH 3 C Cl + H 2 O CH 3 CO 2 H + HCl acetyl chloride The rate of the reaction can be defined as the change of the reactant concentration over a certain time interval. 155

36. Consider the reaction: O CH 3 C Cl + H 2 O CH 3 CO 2 H + HCl acetyl chloride The rate of the reaction can be defined as the change of the reactant concentration over a certain time interval. 156

37. Consider the reaction: O CH 3 C Cl + H 2 O CH 3 CO 2 H + HCl acetyl chloride The rate of the reaction can be defined as the change of the reactant concentration over a certain time interval. That is: 157

38. Delta notation: 158

39. Delta notation: Often the initial time is taken as zero seconds. 159

40. Note that the negative sign in the definition is to ensure that the rate is a positive quantity. 160

41. Note that the negative sign in the definition is to ensure that the rate is a positive quantity. The concentration of the CH 3 COCl is decreasing, so is a negative quantity, hence the negative sign is needed to make the rate positive. 161

42. When the stoichiometric coefficients are not equal to unity, they need to be explicitly taken into account in the definition of the rate. 162

43. When the stoichiometric coefficients are not equal to unity, they need to be explicitly taken into account in the definition of the rate. For the generic reaction: a A + b B c C + d D 163

44. When the stoichiometric coefficients are not equal to unity, they need to be explicitly taken into account in the definition of the rate. For the generic reaction: a A + b B c C + d D the rate is given by 164

45. Example: 2 HI (g) H 2(g) + I 2(g) 165

46. Example: 2 HI (g) H 2(g) + I 2(g) The rate of reaction in terms of HI is 166

47. Kinetic data for the hydrolysis of acetyl chloride. Time (sec) [CH 3 COCl] [CH 3 CO 2 H] 0 1.20 0 2.0 1.05 0.15 4.0 0.93 0.27 6.0 0.81 0.39 8.0 0.71 0.49 10.0 0.63 0.57 ---------------------------------------------------------------- From the above date, the rate over the first 4 second interval is: 167

48. (0.93 – 1.20) M rate = - 4.0 s = 0.068 Ms -1 168

49. (0.93 – 1.20) M rate = - 4.0 s = 0.068 Ms -1 If you calculate the rate over the same time interval at later times you will find the rate of reaction is not constant. 169

50. (0.93 – 1.20) M rate = - 4.0 s = 0.068 Ms -1 If you calculate the rate over the same time interval at later times you will find the rate of reaction is not constant. For most reactions, the rate constant does not remain constant as the reaction progresses. 170

51. (0.93 – 1.20) M rate = - 4.0 s = 0.068 Ms -1 If you calculate the rate over the same time interval at later times you will find the rate of reaction is not constant. For most reactions, the rate constant does not remain constant as the reaction progresses. The above calculation of the rate constant is unsatisfactory in the sense that it only gives us average rates. 171

52. C 2 H 4(g) + O 3(g) C 2 H 4 O (g) + O 2(g) 172

53. In practice, we are interested mainly in the rate of a reaction at a specific time, and not in the average rate, which is arbitrary – because its value depends on the time interval we choose. 173

54. In practice, we are interested mainly in the rate of a reaction at a specific time, and not in the average rate, which is arbitrary – because its value depends on the time interval we choose. We can eliminate this arbitrariness by calculating the rates over smaller and smaller time intervals. 174

55. In practice, we are interested mainly in the rate of a reaction at a specific time, and not in the average rate, which is arbitrary – because its value depends on the time interval we choose. We can eliminate this arbitrariness by calculating the rates over smaller and smaller time intervals. When the time interval is made infinitesimally small, the rate becomes the slope of the concentration versus time plot (at a specific time). 175

56. The hydrolysis of acetyl chloride can also be studied by monitoring the build-up of acetic acid with time. In this case the rate is given by: 176

57. The hydrolysis of acetyl chloride can also be studied by monitoring the build-up of acetic acid with time. In this case the rate is given by: Note that for a rate expressed in terms of a product concentration, we do not need a minus sign on the right-hand side of the equation. 177

58. The hydrolysis of acetyl chloride can also be studied by monitoring the build-up of acetic acid with time. In this case the rate is given by: Note that for a rate expressed in terms of a product concentration, we do not need a minus sign on the right-hand side of the equation. In this case is a positive quantity (the concentration of acetic acid is increasing as the time increases). 178

59. Rate Laws 179

60. Rate Laws The rate of a reaction can be expressed in a second way. For the hydrolysis of acetyl chloride, we can write 180