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Chapter 9. Thermochemistry

Chapter 9. Thermochemistry - Chapter 9 Thermochemistry...

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Chapter 9: Thermochemistry VanKoppen In Chemistry 1A, we have been concerned with the quantitative description of reaction systems. We have expressed the tendency of reactants to be converted to products in terms of the equilibrium constant K for the reaction. Now we question why some reactions have large equilibrium constants while other reactions have small equilibrium constants. The goal of chemical thermodynamics is to predict what types of chemical and physical processes are possible and under what conditions. Thermodynamics can also suggest ways in which conditions can be changed to make a process possible. It can tell us if a process can occur, but it cannot tell us how fast it will occur. Thermodynamic reasoning is based on few apparently simple laws. These laws are not derived . Instead, they are generalizations that have been drawn from a vast number of observations of the way matter behaves. Note that thermodynamics is concerned only with the macroscopic properties of matter that, in principle, can be measured (such as temperature, pressure, volume, etc.). It does not depend on any particular model of the structure of matter such as atomic theory of matter. Chapter 9 covers the fundamental concepts of energy; the chemistry of energy production and exchange. First Law of Thermodynamics (the law of conservation of energy): The energy of the universe is constant. The First Law stated mathematically: E = q + w where E = change in the system's internal energy, q = heat and w = work Our convention will be to take the system’s point of view : By definition: q > 0 => heat is added to the system q < 0 => heat is lost by the system w > 0 => work is done on the system w < 0 => work is done by the system E > 0 => the system gains energy E < 0 => the system loses energy The system's internal energy, E, can be changed by a flow of work, or heat or both work and heat . Energy = Capacity to do work or to produce heat. Heat involves the transfer of energy between two objects. Work = force acting over a distance (work = force x distance). The System is that part of the universe on which attention is to be focused and the Surroundings is everything else in the universe. For example, in considering the reaction for the combustion of methane, we define the system as the reactants and products of the reaction. The surroundings consist of the reaction container, the room, and everything else other than the reactants and products.
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