Chapter_06_Outline - Chapter 6: Thermochemistry After a...

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Chapter 6: Thermochemistry After a consideration of energy and definitions of some basic terms, the relationship between heat, work, and internal energy—the first law—is described. The first law is applied to heats of reactions, after these heats first are determined with calorimetry, leading to Hess’s law. The determination of heats of reaction is simplified with the use of standard enthalpy changes of formation. Consideration of the energy changes involved in combustion and respiration concludes the chapter. Summary/objective of Sections 6.1 Energy Potential and kinetic energies are both defined, along with units of energy: J, kJ, cal, and kcal. O BJECTIVE : Define kinetic and potential energy. 6.2 Thermochemistry: Some Basic Terms Within this section are defined a number of terms: system (open, closed, and isolated); surroundings; internal energy; thermal energy; chemical energy; heat; thermal equilibrium; exothermic; endothermic; work; and pressure-volume work. OBJECTIVE: Define the following: system and surroundings, heat, and work. 6.3 Internal Energy ( U ), State Functions, and the First Law of Thermodynamics A statement of the law of conservation of energy leads to the summary equation: Δ U = q + w. Positive heat and work transfer energy into the system, while negative values transfer energy out of the system. Although absolute internal energy cannot be determined, changes in it can be determined, and these changes depend only on starting and ending conditions, because internal energy is a state function. Heat and work, on the other hand, are path functions, a distinction that is enhanced with a mountain-climbing analogy. OBJECTIVES: State the first law of thermodynamics and know how to apply it. Describe what is meant by a state function. 6.4 Heats of Reaction and Enthalpy Change, H Δ Heat of reaction is the quantity of heat absorbed during a chemical reaction: exothermic if heat is given off (q< 0) and endothermic if heat is absorbed (q > 0). The work involved in most chemical reactions is pressure-volume work, w = - P Δ V and so the heat absorbed at constant pressure is the change in a state function, termed the enthalpy change . Enthalpy change is related to chemical reactions by assuming that each chemical formula in the reaction stands for the amount in moles of that reagent. Thus, multiplying the reaction multiplies the value of H Δ , and reversing the reaction changes the sign of H Δ . OBJECTIVE: Define enthalpy and calculate enthalpy changes. 6.5 Calorimetry: Measuring Quantities of Heat After heat capacity, molar heat capacity, and specific heat are defined, instructions are given on measuring them, along with sample calculations. This leads to measuring heats of reaction in solution. Bomb calorimeters measure the heats of reactions involving gases.
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This note was uploaded on 04/06/2011 for the course CHEMISTRY 161 taught by Professor Seigel during the Fall '10 term at Rutgers.

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Chapter_06_Outline - Chapter 6: Thermochemistry After a...

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