Chapter 11: Thermochemistry – Heat and Chemical Change 11.1 The Flow of Energy – Heat 11.2 Measuring and Expressing Heat Changes 11.3 Heat in Changes of State 11.4 Calculating Heat Changes

11.1 The Flow of Energy - Heat Energy Transformations Thermochemistryis the study of heat changes that occur during chemical reactions. Energy and chemical potential energy Heat (q): Energy that is transferred from one object to another because of a temperature difference between them.

11.1 The Flow of Energy – Heat (cont.) Exothermic and Endothermic Processes Keeping track of terms: system and surroundings. The system is where the action is taking place. The surroundings are everything else! Keep the Law of Conservation of Energy in mind when studying thermochemistry.

11.1 The Flow of Energy – Heat (cont.) Exothermic and Endothermic Processes (cont.) Exothermic processes are those in which heat is released to the surroundings (-q). Examples: hot pack, thermite! campfire, etc. Endothermic processes are those in which heat is absorbed from the surroundings (+q). Examples: cold pack, refrigerator, etc.

11.1 The Flow of Energy – Heat (cont.) Heat Capacity and Specific Heat Burning calories! calorie: the quantity of heat needed to raise the temperature of 1 g of water 1 degree celsius. 1000 calories = 1 Calories = 1 kcal Calories and joules: 1 cal = 4.184 J or 1 J = .2390 calories

11.1 The Flow of Energy – Heat (cont.) Heat Capacity and Specific Heat (cont.) Heat Capacity (C): amount of heat needed to increase the temp. of an object exactly 1 degee celsius. Greater mass = greater C Table 11.2 Heat capacity = specific heat C = q / m x D T

11.2 Measuring and Expressing Heat Changes Calorimetry The accurate and precise measurement of heat changes. Enthalpy(H): heat content of a system. DH = negative, exothermic DH = positive, endothermic Calorimeters

11.2 Measuring and Expressing Heat Changes (cont.) Thermochemical Equations Determining heat changes in a chemical reaction. Figure 11.11 Table 11.4 Calculating heats of reaction (DH) in general and heat of combustion in particular.

Chapter 11 Assignment CPQ 1 pg. 322 # 36,39,40,41,42,43,44,45,47,51

11.3 Heat in Changes of State Heats of Fusion and Solidification What happens when ice melts? Freezes? Molar heat and fusion and solidification: Heat gained or lost when one mole of a substance melts or freezes. Figure 11.13 Table 11.5

11.3 Heat in Changes of State (cont.) Heats of Vaporization and Condensation Sound familiar? The heat gained or lost when 1 mole of a substance vaporizes or condenses. Table 11.5 Heat of Solution Heat change when one mole of a substance dissolves in solution. Can be either exothermic or endothermic.

11.4 Calculating Heat Changes Hess’s Law Calculating heat changes can be as simple as burning a peanut, or using a calorimeter. What if the change is dangerous to measure or takes a long time? Or is complicated? Hess’s Law. Graphite to diamond…

11.4 Calculating Heat Changes (cont.) Standard Heats of Formation Just another way to measure a heat change that may be difficult to do another way. Heat of formation (DHfo). DHfo is defined as the heat change due to the formation of 1 mole of a compound from its individual elements. DHo = DHfo (products) – DHfo (reactants) Table 11.6

Chapter 11 Assignments CPQ 1 pg. 322 CPQ 2 pg. 322 # 36,39,40,41,42,43,44,45,47,51 CPQ 2 pg. 322 # 53,55,56,58,60,62