Chapter6 - Chapter 6: Thermochemistry Chemical reactions...

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Chapter 6: Thermochemistry Chemical reactions obey 2 laws: conservation of mass (previous chapters) conservation of energy (this chapter) 6.1 Energy and Types of Energy A. Definitions Energy - capacity to do work Work - (physicists) force x distance (chemists definition) directed energy change resulting from a process B. Types of Energy 1. Kinetic Energy - energy produced by moving object K.E = ½ mv 2 where m = mass and v = velocity 2. Radiant energy - (solar energy) energy from the sun; from chemical reactions of the sun; affect weather and plant growth 3. Thermal energy - associated with random motion of atoms and molecules. may be calculated from the temperature and amount of molecules Example: cup of coffee at 70 ° C has less thermal energy than a bathtub of water at 40 ° C 4. Potential Energy - energy available by virtue of an objects position, e.g., rock at the top of a cliff 5. Chemical Energy - energy stored in bonds; potential energy associated with chemical bonds: bond breaking: energy is required bond making: energy is liberated All forms of energy may theoretically be converted to other forms of energy. Law of Conservation of Energy - the total quantity of energy in the Universe is constant.
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2 Chapter 6 Chemistry 1303 6.2 Energy Changes in Chemical Reactions These are as important as the mass changes, e.g., combustion of hydrocarbons is done to make use of the energy liberated in the reaction. 1. Heat - (generally the form of energy in chemical reactions) transfer of thermal energy between two bodies at different temperatures: hotter → colder 2. Thermochemistry - study of heat changes in chemical reactions 3. System - part of the Universe of interest to us (beaker, automobile. ....) 4. Surroundings - rest of the Universe 5. Types of Systems : open system - exchanges mass and energy (usually heat) with surroundings; e.g., open beaker of H 2 O (water can evaporate) closed system - allows heat transfer, not mass transfer; e.g. beaker with lid isolated system - allows no heat or mass transfer; e.g., insulated beaker with a lid 6. Exothermic process - gives off heat transfers heat to surroundings heat is essentially a product of the reaction system warms up 7. Endothermic process - heat must be supplied by the surroundings heat is essentially a reactant system cools off 6.3 Introduction to Thermodynamics Thermodynamics – (broader than thermochemistry) scientific study of the interconversion of heat and other kinds of energy 1. State Functions - state of a system – defined by macroscopic properties, i.e. composition, energy, temperature, pressure, volume our concern – change in the system from the point of initial and final states so if the volume changes we want to know Δ V = V f - V i
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3 Chapter 6 Chemistry 1303 First Law of Thermodynamics E nergy can be converted from one form to another, but cannot be created or
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This note was uploaded on 08/22/2011 for the course CHEM 101 taught by Professor C during the Spring '11 term at University of Texas at Dallas, Richardson.

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Chapter6 - Chapter 6: Thermochemistry Chemical reactions...

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