Precipitation is NOT a chemical change.
Precipitation is not a chemical change, but rather a physical change from one state of matter to another. Precipitation begins as water vapor inside a cloud and then condenses into liquid water, which falls to Earth (1).
During a chemical reaction, molecular bonds are broken and rearranged. The substances, which result from a chemical reaction, have different properties from the original chemicals that went into the reaction. A good example of a chemical change is the combustion of gasoline. Combustion occurs when gasoline is mixed with oxygen in the presence of a spark. The hydrocarbons in the gasoline break apart and combine with oxygen to produce carbon dioxide, heat and water vapor. The waste products of combustion have very different chemical properties from the gasoline and oxygen, and the reaction cannot be reversed (2).
States of Matter
On Earth, there are three states of matter: gas, liquid, and solid. Water commonly exists in all three forms. The transition from one state to another does not require the rearranging of molecules or chemical bonds, and the process is completely reversible. For instance, the molecules in gaseous water are not fundamentally changed as they condense into a liquid. The only change is in the kinetic energy of the molecules: the molecules in a gas move fast and freely, whereas the molecules in a liquid are slower and more tightly held together (3).
(1) “Precipitation.” NWS JetStream –. N.p., n.d. Web. 23 Jan. 2013. <http://www.srh.weather.gov/srh/jetstream/synoptic/precip.htm>.
(2) “Chemistry : Amrita Online Lab.” Chemistry : Amrita Online Lab. N.p., n.d. Web. 23 Jan. 2013. <http://amrita.olabs.co.in/?sub=73>.
(3) “States of Matter.” States of Matter. N.p., n.d. Web. 23 Jan. 2013. <http://www.chem.purdue.edu/gchelp/atoms/states.html>.