大学化学课件_国外原版教材_5.pptVIP

Copyright 1999, PRENTICE HALL Chapter 5 Thermochemistry The Nature of Energy Kinetic and Potential Energy From Physics: Force is a push or pull on an object. Work is the product of force applied to an object over a distance: w = F ? d Energy is the work done to move an object against a force. Kinetic energy is the energy of motion: The Nature of Energy Kinetic and Potential Energy Potential energy is the energy an object possesses by virtue of its position. Potential energy can be converted into kinetic energy. Example: a ball of clay dropping off a building. First Law of Thermodynamics Internal Energy Internal Energy: total energy of a system. Cannot measure absolute internal energy. Change in internal energy, DE = Efinal - Einitial Hess’s law: if a reaction is carried out in a number of steps, ?H for the overall reaction is the sum of ?H for each individual step. For example: CH4(g) + 2O2(g) ? CO2(g) + 2H2O(g) ?H = -802 kJ 2H2O(g) ? 2H2O(l) ?H = -88 kJ CH4(g) + 2O2(g) ? CO2(g) + 2H2O(l) ?H = -890 kJ Enthalpies of Formation If 1 mol of compound is formed from its constituent elements, then the enthalpy change for the reaction is called the enthalpy of formation, ?Hof . Standard conditions (standard state): 1 atm and 25 oC (298 K). Standard enthalpy, ?Ho, is the enthalpy measured when everything is in its standard state. Standard enthalpy of formation: 1 mol of compound is formed from substances in their standard states. If there is more than one state for a substance under standard conditions, the more stable one is used. Enthalpies of Formation Standard enthalpy of formation of the most stable form of an element is zero. Enthalpies of Formation Enthalpies of Formation * Chapter 5 David P. White University of North Carolina, Wilmington The Nature of Energy Energy Units SI Unit for energy is the joule, J: We sometimes use the calorie instead of the joule: 1 cal = 4.184 J (exactly) A nutritional Calorie: 1 Cal = 1000 cal = 1 kcal The Nature of En