Lecture 12 - Lecture 12. The liquid state Almost all...

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Lecture 12. The liquid state Almost all chemical reactions occur in liquids! In gases, the collisions are too infrequent (the concentrations are too small) for reactions to occur a reasonable rates. In solids, the collisions are essentially nonexistent. We focus on liquids both as phases on the way to solids, and as media for chemical reactions. The structure of liquids Liquids have a fairly constant density, much higher than that of gases (smaller volume than gases Liquids do not hold their shape, but instead fill their container. They cannot easily conform to a change in container volume, but do conform to container shape. Molecules have some kinetic energy Liquids are held together by polar forces (including H-bonds), but not in any particular direction or arrangement At this point, we can’t really understand any more about why liquids form or what their properties are without returning to the terms enthalpy and entropy. Enthalpy is a measure of the capacity to do work: H = E + PV (all in units of energy) is often similar to E, and is inversely correlated to stability is a state function, meaning it is a property of a system that is independent of the previous history of the system is an extensive property, meaning that it is proportional to the number of members of the system. It is convenient, but not necessary, to refer to enthalpy per mole of molecules, bonds, electrons, etc. is the amount of heat+work transferred in a process that is reversible minimizing H is a driving force for transforming a system Enthalpy and chemical transformations An exothermic transformation gives off heat (work) to the surroundings. The change in enthalpy ΔH is negative. Where the number of possible configurations of the system does not change during the transformation, the system becomes
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Lecture 12 - Lecture 12. The liquid state Almost all...

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