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7 - GENERAL CHEMISTRY Principles and Modern Applications...

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1 GENERAL CHEMISTRY Principles and Modern Applications PETRUCCI HERRING MADURA BISSONNETTE PETRUCCI HERRING MADURA BISSONNETTE Thermochemistry 7 Chemical Changes and Energy Redistribution Chemical changes are accompanied by redistribution of energy as well as matter redistribution of energy, as well as matter EXAMPLE : Energy that keeps us alive (metabolism of foods) C 6 H 12 O 6 (s) + 6 O 2 (g) 6 CO 2 (g) + 6 H 2 O(g) + energy Other examples include: Combustion of fuels (feels hot) Mixing an acid solution with a base solution (feels hot) Dissolution of ammonium nitrate in water (feels cold),... Chemical Changes and Energy Redistribution Chemical changes are accompanied by redistribution of energy as well as matter redistribution of energy, as well as matter Energy Flows Between System and Surroundings The System, the Surroundings, the Universe The system represents the object or the collection of objects being studied The surroundings represent everything outside of the system system + surroundings = universe
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2 Energy Flows Between System and Surroundings FIGURE 7-1 Systems and their surroundings Energy: Its Forms and Transformations ENERGY IS DEFINED AS THE CAPACITY TO DO WORK Energy can be classified as kinetic energy or potential energy . Kinetic energy is the energy of a moving object (in thermo chemistry the moving objects are particles such as atoms, molecules or ions and motion includes translation, vibration and rotation of particles). Potential energy results from the position of objects (it is the energy associated with forces of attraction or repulsion between particles) Kinetic Energy 1 2 [ ] m J k 2 e k = 2 mv e k ] = s = kg w = F x d Work w F d = m x a x d [ w ] = m s 2 = J m kg Energy: Its Forms and Transformations Energy can be converted from one form to another. Potential energy is converted to kinetic energy during the dive. On entering the water, the kinetic energy is converted into mechanical energy of waves and increased kinetic energy of water molecules.
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