what are metastable energy states?
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"Somewhat stable" energy level. The length of time an electron can be expected to reside in a metastable energy level (lifetime) is much greater than the time it can be expected to reside in other excited states. The lifetime to a metastable state is typically 10-3 seconds while the lifetime for other excited states is typically 10-8 seconds.\n\nAnswer to second question can be found in the definition of a Laser. \n\nAn acronym of Light Amplification by Stimulated Emission of Radiation. A laser is a cavity that has mirrors at the ends and is filled with lasable material such as crystal, glass, liquid, gas, or dye. These materials must have atoms, ions, or molecules capable of being excited to a metastable state by light, electric discharge, or other stimulus. The transition from this metastable state back to the normal ground state is accompanied by the emission of photons that form a coherent beam.\n\nSo my take on it?  Metastable energy levels are required for electrons to emit photons,  and being that metastable energies are more stable than other excited levels, they are more useful in industrial applications.  So Lasers use this phenomenon to project a beam of photons that are still particles.
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Basically, energy is conserved in a system; it is always the same.   Heat, volume, and pressure (volume/pressure = work) can all change and you can still maintain the same internal energy of the system.  A state function is a property of a system that depends only on the current state of the system, not on the way in which the system got to that state, therefore energy is a state function.  Heat and work are not because they simply describe the way in which the system REACHED equilibrium, not the system AT equilibrium
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http://en.wikipedia.org/wiki/Eigenstate
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the condition of an atom or molecule after absorbing energy from exposure to light, electricity, elevated temperature, or a chemical reaction, and which may be a necessary prelude to a chemical reaction or to the emission of light.\n\nExcited state \nIn quantum mechanics, a stationary state of higher energy than the lowest stationary state or ground state of a particle or a system of particles. Customarily, only bound stationary states, which generally are at most denumerably infinite in number, are spoken of as excited, although the formal quantum theory often treats the noncountable unbound stationary states on an equal footing with the bound states
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When heated the electrons move from the ground state to an exicited state.  They are unstable here and return to the ground state giving off energy in the form of a specific color.  Different energy levels will produce different colors
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Density Matrix.\n\ndiagonal part + nondiagonal part or\nstate probabilities + transition probabilities.
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Negative energy can refer to several concepts:\n\n    * Negative rest energy, which corresponds to negative mass, which has many unusual physical consequences.\n    * Energy in any system below the conventionally-defined ground state. Examples are positrons under the dirac sea model of electron behavior, and the region of reduced vacuum energy associated with the Casimir effect. This type of effect typically occurs under exotic or unexpected conditions, as the definition of the ground state is usually chosen because it is the state of lowest expected energy within a system.\n    * Energy in any system below an arbitrarily defined zero level. Examples include electron potential energy within an atom under the Bohr model of atomic structure, and gravitational potential energy in Newton's model of gravity.
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Potential & Kinetic are the 2 types of energy. Potential energy is energy that is stored in an object. If you stretch a rubber band, you will give it potential energy. As the rubber band is released, potential energy is changed to motion. Kinetic energy is energy of motion. A rubber band flying through the air has kinetic energy. When you are walking or running your body is exhibiting kinetic energy. Potential energy is converted into kinetic energy.
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All atoms have intermolecular forces that keep them together as solids or liquids. Adding energy will overcome these forces and cause them to change phase from solid->liquid->gas (with a few that jump straight from solid to gas).\n\nEnergy has to be added to cause this phase change. Going in the opposite direction requires withdrawing energy.\n\nThe types of forces or bonds (not chemical bonds) absorb energy when broken, give up energy when formed. It implies that the solids are in a lower energy state than liquids, and liquids lower than gases.\n\nThis said, when water turns in ice, heat energy is being withdrawn, and the molecules are getting into a more stable and fixed configuration with respect to each other. Because of the polar nature of water, it forms hydrogen bonds between molecules. These type of bonding means when water turns into ice, it positions the molecules into very specific configurations, to maintain the lowest energy state it can get to. Hence the formation of ice crystals.
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You have to specify the energy migration profile. Either adiabatic (zero energy transfer) or iso-volumetric (a lot of energy entering the system) or something in between.\n\nAlso, you have to specify the thermal units (Celsius/Fahrenheit/Kelvin/Rankin).
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at 0K, vibrational movements of atoms stop ... this means that atoms are completely stationary - in other words, they have no energy ... this state is known as absolute zero.
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Hey check this out, I guess there are 7 states.\n\nThese phases include gases, plasmas, liquids, fluids, superfluids, solids, and Bose-Einstein condensates.\n\nSorry about all the rephrasing.
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Many forms of energy exist around us. Energy cannot be created or destroyed, only changed from one form to another. If a person ever says that energy is lost, what really happens is that energy is spent or changed into different forms. It never really is lost. For example, if you use water energy to create mechanical energy, you might "lose" some energy by creating heat energy in the form of friction.
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Electrons absorb energy to move from a lower level to a higher one.  They release energy going from higher to lower.
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The change of energy  between energy levels.\n\nEnergy of electron in it's higher state  - energy of electron in it's lower state = h*f\n\nI forgot how to calculate the electron's energy at a specific energy state, but it should be easy to find.
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Ground State - 1s2 2s2 2p6 3s1 : 2,8,1\n\nElectron moves from the 2p orbital into the 3s orbital.\nExcited State - 1s2 2s2 2p5 3s2 : 2,7,2
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If you're talking about a thermodynamically endothermic rxn, then PHOTOSYNTHESIS is a good example. Photosynthesis needs to be powered by solar energy in order to work. All endothermic processes need energy INPUT to urn. Conversely, exothermic rxns can happen spontaneously and release energy as product.