Lect%206%20Thermochemistry-08

Lect%206%20Thermochemistry-08 - Thermochemistry Energy Flow...

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Thermochemistry Energy Flow and Chemical Change Thermodynamics is concerned with the relationship between heat and other forms of energy. “Keeping track of Energy Transfer” Thermochemistry is the study of the quantity of heat absorbed or evolved by chemical reactions.
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The Law of Conservation of Energy: Energy may not be created or destroyed but only converted from one form to another. i.e. the total quantities of energy remain constant. First Law of Thermodynamics
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Energy Energy can be encountered in many forms: Radiant Energy -Electromagnetic radiation. Thermal Energy - Associated with random motion of a molecule or atom. Chemical Energy - Energy stored within the structural limits of a molecule or atom.
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Kinetic Energy is the energy associated with an object by virtue of its motion. Potential Energy is the energy an object has by virtue of its position in a field of force. Internal Energy is the sum of the kinetic and potential energies of the particles making up a substance. Three main energy concepts:
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Kinetic Energy An object of mass m and speed or velocity v has kinetic energy E k equal to i.e. the kinetic energy of an object depends on both its mass and its speed. 2 2 1 k mv E
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Potential Energy. Depends on the “position” (such as height) in a “field of force” (such as gravity). For example, water of a given mass m at the top of a dam is at a relatively high “position” h in the “gravitational field” g of the earth. mgh E p
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Problem What is the kinetic energy of a person whose mass is 130 lb (59.0 kg) traveling in a car at 60 mph (26.8 m/s)? 2 2 1 k ) s / m 8 . 26 ( ) kg 0 . 59 ( E The SI unit of energy, kg . m 2 /s 2 , is the Joule . 2 2 4 k s / m kg 10 12 . 2 E J 10 12 . 2 E 4 k
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Internal Energy is the energy of the particles making up a substance. (motion of electrons, bond energies, electrostatic interactions between molecules….) The total energy of a system is the sum of its kinetic energy, potential energy, and internal energy, U . U E E E p k tot
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In chemical reactions, heat is often transferred from the “system” to its “surroundings,” or vice versa. The substance or mixture of substances under study in which a change occurs is called the thermodynamic system ( or simply the system . ) The surroundings are everything outside of the thermodynamic system. System and Surroundings
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Heat is defined as the energy that flows into or out of a system because of a difference in temperature between the system and its surroundings. Heat flows from a region of higher temperature to one of lower temperature; once the temperatures become equal, heat flow stops.
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Heat is denoted by the symbol q. The sign of q is positive if heat is absorbed by the
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Lect%206%20Thermochemistry-08 - Thermochemistry Energy Flow...

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