Chemical reactions occur so that atoms gain stability. For example, oxygen will react with carbon because the product, carbon dioxide, has more chemical stability - in other words, each atom shares its electrons to give the other atom(s) in the molecule an electron arrangement of more stability that the one before.
When atoms and molecules speed up or slow down, that is a physical change. When they change state from liquid to solid or from gas to liquid, that is a physical change. When a substance is dissolved by water or some other solvent, a new substance has not really been formed. The ions or molecules can still come back together to form the original substance. In most chemical reactions, two or more substances, called reactants, interact to create different substances called products. A reaction is following a fundamental law of nature (enthalpy-its the nature of things to want to use the smallest amount of energy possible, so when a reaction can occur that produces more energy, it will. Also, entropy-its the nature of things to be as disorganized as possible, such as the breaking down or decomposing of material).
Chemical reactions describe the changes between reactants (the initial substances that enter into the reaction) and products (the final substances that are present at the end of the reaction). Describing interactions among chemical species, chemical reactions involve a rearrangement of the atoms[->0] in reactants to form products with new structures in such a way as to conserve atoms. Chemical equations are notations that are used to concisely summarize and convey information regarding chemical reactions. In a balanced chemical reaction all of the matter[->1] (i.e., atoms or molecules) that enter into a reaction must be accounted for in the products of a reaction. Accordingly, associated with the symbols for the reactants and products are numbers (stoichiometry coefficients) that represent the number of molecules, formula...
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