Chapter 11: Thermochemistry – Heat and Chemical Change

11.1 The Flow of Energy – Heat11.2 Measuring and Expressing

Heat Changes11.3 Heat in Changes of State11.4 Calculating Heat Changes

11.1 The Flow of Energy - Heat

Energy Transformations Thermochemistry

is 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 T

11.2 Measuring and Expressing Heat Changes

Calorimetry The accurate and

precise measurement of heat changes.

Enthalpy(H): heat content of a system. H = negative,

exothermic H = positive,

endothermic Calorimeters

11.2Measuring and Expressing Heat Changes (cont.)

Thermochemical Equations Determining heat changes in a chemical

reaction. Figure 11.11 Table 11.4 Calculating heats of reaction (H) 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 (Hf

o).

Hfo is defined as the heat change due to

the formation of 1 mole of a compound from its individual elements.

Ho = Hfo (products) – Hf

o (reactants) Table 11.6

Chapter 11 Assignments

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

CPQ 2 pg. 322 # 53,55,56,58,60,62