Energy: The capacity to do work or supply heat. This capacity exists in either a stored potential or an active motion. |
Stored energy is call potential energy. PE is related to position of shared electrons in covalent bonds. |
When shared electrons are far from the nuclei, the bond is long and weak. |
If the electrons are closer to one or both of the atoms, the bond becomes shorter and stronger. |
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Greater capacity to be broken apart and reform into new, strong bonds |
Less capacity to be broken apart |
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MORE PE/Chemical E |
LESS PE/Chemical energy |
Energy of motion- kinetic energy |
Kinetic energy of molecular motion- thermal energy |
1st law of thermodynamics: E cannot be either created or destroyed, only transferred |
Endothermic |
"within heating" |
Thermal E absorbed by system |
Exothermic |
"outside heating" |
Thermal E released by system |
Spontaneous chemical reactions- able to proceed on their own without any continuous external influence, such as added E. |
2 factors determine this- |
1. Rxn's tend to be more spontaneous when the product molecules are less ordered than the reactant molecules. |
2. Rxn's tend to be spontaneous if products have lower PE than the reactants. |
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The amount of disorder in a system is called Entropy. |
When the shared electrons in the reaction products are held more tightly than those in the reactants. |
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Increased Entropy in products = Increased spontaneity |
Lower PE in products than the reactants |
Reactants |
--------- |
Products |
Entropy |
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Entropy |
Order |
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Order |
PE |
|
PE |
capacity for bonds to break & form stronger bonds |
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capacity for bonds to break & form stronger bonds |
Long, loose, weak bonds |
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Short, tight, strong bonds |
