C1210 lecture 13

C1210 lecture 13 - Energy: making and breaking chemical...

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Energy: making and breaking chemical bonds: What is energy? You can’t see it. You can’t feel it. You can’t taste it. You can’t detect it directly. You CAN sense its effects It can do work. It can supply heat. It can also be transferred as light or radiation. Definition : Energy is the ability to do work. Temporary effective definition : work is motion against an opposing force. “Opposing force”: Lift a weight. Expand a balloon. Stretch a spring. Push molecules that repel each other closer than they want to be. Pull molecules that attract one another apart.
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Types of energy: Definition : kinetic energy; the energy associated with motion. 2 2 1 . . mv E K = fast atom slow atom slower fast atom less energy faster slow atom more energy Conservation of energy
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Types of energy: Definition: potential energy; energy associated with an object’s position: Raise or lower an object against gravity. Compress or stretch a spring. Swing a pendulum. Change the distance between electrons and protons . Nucleus Electron Nucleus Electron distance d lower potential energy distance 3d higher potential energy Push or pull against the opposing force: raises energy. Push or pull with the opposing force: lowers energy. Bound energy is < 0.
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Converting kinetic and potential energy; a pendulum: Maximum kinetic energy Minimum potential energy Minimum kinetic energy Maximum potential energy
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Converting kinetic and potential energy; masses connected by a spring: Equilibrium: no potential energy, no kinetic energy (not moving). Fully compressed or fully stretched: Minimum kinetic energy Maximum potential energy Halfway compressed or stretched: maximum kinetic energy, minimum potential energy; similar to equilibrium (but moving). Law of conservation of energy: energy cannot be created or destroyed, it can only be changed from one form to another.
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Heat and temperature: NOT the same thing. In all gases, liquids and solids, the atoms and ions are moving and colliding with each other they have kinetic energy. All atoms and ions don’t have the same kinetic energy, some are fast, some are slow, but the temperature is defined by the average kinetic energy. Increase the temperature, increase the average kinetic energy. Heat (thermal energy) spontaneously flows from high temperature objects to low temperature objects. Collisions occur, energy is exchanged, faster particles leave collisions slower and slower particles leave collisions faster. The average velocity of the slowed particles drops and the average velocity of
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This note was uploaded on 12/10/2009 for the course CHE 1220 taught by Professor Jespersen during the Spring '09 term at St. John's.

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C1210 lecture 13 - Energy: making and breaking chemical...

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