Hobbies And Interests
Color
Something as natural as leaf color change in autumn signals chemical change. When paper burns, it turns to black and eventually to gray ash. When wood burns, it glows red. These and many other color changes signal the reorganization of elements within a substance to form another substance that possesses a different physical and chemical configuration. Iron and sulfur filings, when mixed and heated, chemically change to a non-magnetic grey substance. Simply mixing them may alter the color somewhat, but the components are still magnetically separable, thus making it a physical change.
Odor
Odor alteration can signal chemical change. Atomic restructuring creates substances that possess their own distinctive smell. When food spoils, chemicals are produced that have a different odor than unspoiled food. When you spray perfume on your body, the chemicals in the perfume react with your body's chemicals -- such as sweat -- and produce an odor that varies among individuals. The souring of milk and ripening of cheese are both the result of lactic acid fermentation, a chemical process noticeable by odor.
Gas and Solid Formation
Effervescent tablets react with water to produce gas bubbles, as demonstrated by fizzing. This also happens to carbonated sodas. During manufacture of carbonated beverages, carbon dioxide dissolves at a higher pressure than normal. Carbonic acid is formed, which lies inactive within the bottle until it is disturbed by opening and subsequent pressure release, into variable gas molecules and water separation. Carbon dioxide warms to room temperature, rising to the surface to form bubbles due to kinetic energy. Formation of solids occurs when two chemicals react and the ion product has a higher ion concentration than what the solution can readily take in, forming a precipitate. This is typified by the reaction between sodium chloride and silver nitrate, which forms silver chloride insoluble in aqueous solution.
Energy Release or Conversion
Soda fizzing releases kinetic energy that rises upwards in a bottle, which in turn produces the bubbles. The chemical energy in fuel is transformed into mechanical energy to run a vehicle. Cooking stoves convert the chemical energy of cooking gas into heat energy. Photovoltaic (solar) cells convert solar energy to electrical energy.
Temperature Change
An exothermic process produces heat, causing temperature to rise and sometimes cause explosive reactions. Rusting produces thermal heat, although this occurs too slowly to become noticeable. An endothermic process causes a lowering of temperature as heat is absorbed by the substance. This is demonstrated in plant photosynthesis, dissolution of salt in water (salt lowers the freezing and melting points of water), evaporation, melting and boiling.