01a_U3_energy reading-v2.1-1 - ChemistryUnit3 In the 18th...

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Chemistry – Unit 3 Energy and Kinetic Molecular Theory In the 18 th and 19 th centuries scientists wrestled with identifying and describing the nature of the “stuff” that produced change. One concept that became popular for a while was that of “caloric” (what we now call heat). “Caloric was originally conceived of as a quantity that would flow from a hotter object to a cooler one that would warm up as a result. It answered the need for a way for the cause of warming to get from here to there. Not only did caloric serve as a cause for warming, it was also considered to be the cause for changes of phase. Caloric enabled particles of a substance to move farther apart until the attraction of the particles for each other became too weak to hold them together. Although Lavoisier did not think that caloric necessarily was an actual substance, in its storage and transfer it was like a substance. . i When scientists recognized that the “stuff” involved when forces were applied to objects to lift them or change their speed was the same “stuff” that was involved when the temperature of objects changed, they worked to develop a single energy concept. “So when the energy concept was developed it was important to distinguish it from caloric. In snuffing out the caloric concept, the clear picture of energy storage and transfer that it fostered was unnecessarily lost, too.” ii Even though we recognize that energy is not a physical substance, we choose to use the substance metaphor to describe it. We’ll use three principles to guide us in the development of the energy concept. 1. Energy can be viewed as a substance-like quantity that can be stored in a physical system. 2. Energy can “flow” or be “transferred” from one system to another and so cause changes.
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