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UNT CHEM 1415 - Introduction to Energy and Enthalpy
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CHEM 1415 1st EditionLecture 9Unit: Introduction to Energy, Heat Capacity and EnthalpyOutline of Current Lecture I. EnergyII. Heat and WorkIII. Conservation of EnergyIV. Heat Capacity and CalorimetryV. EnthalpyCurrent Lecture Energyo Potential Energy Associated with the relative position of an object The higher an object, the more potential energy it contains due to gravity Attraction and repulsion between electrical charges also leads to potential energyo Kinetic Energy Energy associated with motion When an object is falling, it is converting potential energy to kinetic energyKE=12m v2o Internal Energy Combined kinetic and potential energies of the atoms and molecules that make up an objecto Chemical energy Excess energy released if a chemical in bond breaking does not absorb all of the energy Type of potential energyo More specific forms of energy Radiant energy – associated with light or electromagnetic radiation Mechanical energy – movement of macroscopic objects Thermal energy – temperature of an object  Electrical energy – moving charges Nuclear energy – released in nuclear fusion and fission processesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Units SI unit – joule(J), 1 J = 1kg m2s2 Heat and Worko Heat Flow of energy between two objects, from the warmer one to the cooler one because of difference in temperatures, process not quantityo Work Transfer of energy accomplished by a force moving a mass in a distance Conservation of Energyo System – part of the universe that is being studiedo Surroundings – remainder of the universeo Boundary – separates the system and the surroundingsoE=q+ wo∆ E= Efinal−EinitialoExample 1: 515 J of heat is added to a gas that does 218 J of work, what is the changein energy of the system? q = +515 J and w = -218 J ΔE=q+ w ΔE=515−218 ΔE= 297 Jo 1st Law of Thermodynamics Energy can be transformed between forms but cannot be created or destroyed Heat Capacity and Calorimetryo Calorimetry A set of techniques that observes heat flow into or out of a systemo Specific heat capacity, c Measures how much heat is required to raise the temperature of one gram of that material by 1℃q=mc ∆ T Enthalpyo Heat flow under constant pressure conditions, Ho H = E + PVo Exothermic – heat evolves from a system, ΔH is less than zeroo Endothermic – heat is absorbed by the system, ΔH is greater than


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