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Chapter 5 - Chapter 5 Energy and Chemical Reactions I A...

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Chapter 5: Energy and Chemical Reactions I. Energy A. Definition Energy - capacity to do work B. Types of Energy 1. Kinetic - energy of motion a. Thermal - motion of atoms, molecules, ions b. Mechanical - motion of macroscopic objects, automobile, tennis ball c. Electrical - movement of electrons through a conductor d. Sound - compression and expansion of the spaces between molecules in the transmission of sound. 2. Potential - energy available by virtue of an object's position a. Gravitational - rock at the top of a hill, ball held by a hand b. Chemical - energy stored in the structural units of chemical substances c. Electrostatic - energy associated with the separation of two ions or other charged particles C. Law of Conservation of Energy - the total energy of the universe is a constant, that is, energy cannot be created nor destroyed, only changed from one form to another. D. Other Definitions 1. Heat - transfer of thermal energy between two objects that are at different temperatures 2. Temperature - the measure of the ablility of an object to transfer energy as heat. 3. System - specific part of the universe under study 4. Surroundings - the rest of the universe 5. Open system - can exchange mass and energy (heat) with the surroundings 6. Closed system - allows the transfer of energy, but not mass 7. Isolated system - allows the transfer of neither mass nor energy 1
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8. Directionality of heat transfer - heat is transferred from an object of higher temperature to an object of lower temperature until the temperature of the two objects is the same, that is, until thermal equilibrium is reached. a. Exothermic - heat transfer from system to surroundings b. Endothermic - heat transfer from the surrounding to the system 9. Energy units - joule, J 1 calorie = 4.18 joules II. Specific Heat Capacity: Heating and Cooling A. General Information The amount heat (energy) that is transferred in a process, whether physical or chemical, depends on the: 1. Amount of substance 2. Magnitude of the temperature change 3. Ability of the substance to absorb energy (specific heat capacity) B. Specific Heat Capacity/Energy Change 1. Specific heat capacity (C) - energy required to raise the temperature of 1 gram of substance by one kelvin units: C = J/g K 2. Energy change: q = (C) (m) ( T) q = energy gained or lost C = specific heat capacity m = mass of substance T = change in temperature T = T final - T initial The change in temperature is the same value whether it is expressed in degrees Celcius or in kelvins.
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