Part 7 Chapter 1 Chemistry

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The book was talking about energy from energy as a boulder from the top of a mountain turning into kinetic energy from the gravity and then into a level a lower more stable energy. The book shows cells of energy falling in a Translational falling state to a lower-level Vibrational meeting in the middle and a Rotational state as they are doing a merry-go-round with each other. Then it goes back to review about the types of reactions {Exothermic versus Endothermic}. The book says, "When physical or chemical changes occur, energy is involved. If the heat content of the product(s) is higher than that of the reactants, the reaction is 'endothermic'. If, on the other hand, the heat content of the product(s) is less than that of the reactants, the reaction is 'exothermic'. This change of heat content can be designated as a triangle H. The heat content (H) is sometimes referred to as the enthalpy. Every system has a certain amount of heat that changes during the course of a physical or chemical change. The change in heat content (a triangleH) is the difference between the heat content of the products and that of the reactants. The equation is triangleH=Hproducts-Hreactants. If the heat content of the products is greater than the heat content of the reactants, triangleH is a positive quantity (triangleH>0) and the reaction is endothermic. If, however, the heat content of the products is less than heat content of the reactants, triangleH is a negative quantity (triangleH<0) and the reaction is exothermic." This relationship was shown in Figures 1 and 2 and the topic is developed in detail of chapter 8. Another repeat is in the Conservation of Energy. It says, " Experiments have shown that energy is neither gained nor lost during physical or chemical changes. This principle is known as the 'Law of Conservation of Energy' and is often stated as follows: Energy is neither created nor destroyed in ordinary physical and chemical changes. If the system under study loses energy (the reaction is exothermic and triangleH is negative), the surroundings of the system must gain the energy that the system loses so that energy is conserved. More on Conservation in the next lesson.