Thermochemistry

Thermochemistry - Thermochemistry Dr. N. F. Campbell 1...

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Thermochemistry Dr. N. F. Campbell 1 Thermochemistry Nature of Energy I. Introduction Thermochemistry - the study of energy and its transformation II. Energy Flow 1. Whenever energy is transferred from one object to another, it appears as work and or as heat. w = F x d; energy in the form of work used to move an object against a force. Heat is the energy transferred from a hotter object to a colder object. 2. Energy - the capacity to do work or to transfer heat. III. Kinetic and Potential Energy 1. Kinetic energy is the energy of motion ( E mv k = 1 2 2 ). The energy an object possesses because of its temperature (thermal energy) is associated with the kinetic energy of the molecules in the object. 2. Potential energy is stored energy (the result of attractions and repulsions an object experiences in relation to other objects). An electron has potential energy when it is near a proton due to electrostatic attraction. Many substances, fuels, release energy when they react. This chemical energy is due to potential energy stored in arrangements of atoms of the substance. IV. Units of Energy 1. Joule (J). 1J= 1kg-m 2 -s -2 2. calorie (cal). The amount of energy required to raise the temperature of 1 gram of water by 1 o C. 1 cal = 4.184 J V. Systems and Surroundings 1. System. The part of the universe whose change is being measured 2. Surrounding. Everything else excluding the system that is relevant. 3. Closed system - exchange energy but not matter with its surroundings. 4. Example: Chemical reaction occurring in a beaker; the system consists of the flask’s contents and the surrounding consists of the flask and laboratory. The First Law of Thermodynamics I. Introduction Energy is conserved. The energy of the system plus the energy of the surroundings remains constant ( E universe = E system + E surroundings = 0). Energy lost by system equal energy gained by surrounding or vice versa. Energy can be converted from one form into another as it is transferred, but it cannot be created or destroyed. II. Internal Energy 1. Internal Energy (E). The sum of kinetic and potential energies of all the particles in a system.
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Thermochemistry Dr. N. F. Campbell 2 2. For chemical reaction E = E final - E initial = E products - E reactants 3. If system lose some of its energy to the surrounding, E final < E initial ; E < 0. Place hot water in glass and the glass becomes warmer. 4. If system gain some of its energy from the surrounding, E final > E initial ; E > 0. Place ice in glass and ice melts and glass becomes cooler. 5.
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Thermochemistry - Thermochemistry Dr. N. F. Campbell 1...

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