* Chemical reactions occur when substances undergo chemical changes to form new substances * Production of gas and change of color are sings of chemical reactions * Chemical reactions rearrange atoms
* A reactant is a substance or molecule that participates in a chemical reaction * A product is a substance that forms in a chemical reaction Energy and Reactions
* Energy must be added to break bonds.
* Many forms of energy can be used to break bonds:
* Forming bonds releases energy
* Example: when gasoline burns, energy in the form of heat and light is released as the products of the isooctane-oxygen reaction and other gasoline reactions form. * Energy is conserved in chemical reactions.
* Chemical energy is the energy released when a chemical compound reacts to produce new compounds. * The total energy that exists before the reaction is equal to the total energy of products and their surroundings. * An exothermic reactions is a chemical reaction in which heat is released to the surroundings * An endothermic reaction is a chemical reaction that absorbs heat. * A synthesis reaction is a reaction in which two or more substances combine to form a new compound * Synthesis reactions have the following general form: A + B AB * Example: in the following synthesis reaction, the metal sodium reacts with the chlorine gas to form sodium chloride, or table salt. * 2Na+Cl2 2NaCl
* A decomposition reaction is a reaction in single compound beaks down to form two or more simpler substances. * Decomposition reactions have the flowing form: AB A+B * Example: The following shows the decomposition of water * 2H2o 2H2+O2
* Electrolysis is the process in which an electric current is used to produce a chemical reaction, such as the decomposition of water.