AP Chemistry –Thermodynamics

AP Chemistry –Thermodynamics - AP Chemistry...

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AP Chemistry –Thermodynamics Section 19.1 Change is central to chemistry. When describing changes, chemists use the term spontaneous . A spontaneous change is one that occurs without outside intervention. This statement does not say anything about the rate of the change, merely that a spontaneous change is naturally occurring and unaided. A spontaneous change leads inexorably to equilibrium. Many chemical reactions proceed spontaneously until equilibrium is reached. Some reactions greatly favor products at equilibrium, while others favor reactants. These are known as product-favored and reactant-favored reactions, respectively. When considering both physical and chemical processes, the focus is always on the changes that must occur to achieve equilibrium. A chemical system at equilibrium will not spontaneously change in a way that results in the system no longer being in equilibrium. Neither will a chemical system not at equilibrium change in the direction that takes it farther from the equilibrium condition. Section 19.2 The expansion of gas into a vacuum is spontaneous. Temperature can have a role in determining whether a process is spontaneous. Heat transfer from a hotter object to a cooler object is spontaneous. Equilibrium can be approached spontaneously from either direction. The evolution of heat is not a sufficient criterion to determine whether a process is spontaneous. This makes sense because the first law of thermodynamics tells us that in any process energy must be conserved. If energy is evolved by a system, then the same amount of energy must be absorbed by the surroundings. The exothermicity of the system must be balanced by the endothermicity of the surroundings so that the energy content of the universe remains unchanged. If energy evolution were the only factor determining whether a change is spontaneous, then for every spontaneous process there would be a corresponding nonspontaneous change in the surroundings. Section 19.3 A better way to predict whether a process will be spontaneous is with a thermodynamic function called entropy, S . Entropy is tied to the second law of thermodynamics , which states that in a spontaneous process, the entropy of the universe increases . This law allows us to predict the conditions at equilibrium as well as the direction of spontaneous change toward equilibrium. The concept of entropy is built around the idea that spontaneous change results in dispersal of energy . Many times, a dispersal of matter is also involved, and it can contribute to energy dispersal in some systems.
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AP Chemistry –Thermodynamics The dispersal of energy over as many different energy states as possible is the key contribution to entropy. Even in a simple example with only two packets of energy to consider, it is more likely
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AP Chemistry –Thermodynamics - AP Chemistry...

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