Home

Home
Common Compounds
Exam Guide
FAQ
Features
Glossary
Construction Kits
Companion Notes
Just Ask Antoine!
Simulations
Slide Index
Toolbox
Tutorial Index

FAQ
Introduction
Measurement
Matter
Atoms & ions
Compounds
Chemical change
The mole
Gases
Energy & change
The quantum theory
Electrons in atoms
The periodic table
Chemical bonds
Solids
Liquids
Solutions
Acids & bases
Redox reactions
Reaction rates
Organic chemistry
Everyday chemistry
Inorganic chemistry
Environmental chemistry
Laboratory
History of chemistry
Miscellaneous


Home :FAQ :MatterPrint | Comment
Previous Question Next Question

What is the difference between chemical and physical change?


Britiani

Vocabulary
carbohydrate*
chemical bond*
chemical property*
physical property*
property*
protein*
Chemical change is any change that results in the formation of new chemical substances. At the molecular level, chemical change involves making or breaking of bonds between atoms. These changes are chemical:

  • iron rusting (iron oxide forms)
  • gasoline burning (water vapor and carbon dioxide form)
  • eggs cooking (fluid protein molecules uncoil and crosslink to form a network)
  • bread rising (yeast converts carbohydrates into carbon dioxide gas)
  • milk souring (sour-tasting lactic acid is produced)
  • suntanning (vitamin D and melanin is produced)

Physical change rearranges molecules but doesn't affect their internal structures. Some examples of physical change are:

  • whipping egg whites (air is forced into the fluid, but no new substance is produced)
  • magnetizing a compass needle (there is realignment of groups ("domains") of iron atoms, but no real change within the iron atoms themselves).
  • boiling water (water molecules are forced away from each other when the liquid changes to vapor, but the molecules are still H2O.)
  • dissolving sugar in water (sugar molecules are dispersed within the water, but the individual sugar molecules are unchanged.)
  • dicing potatoes (cutting usually separates molecules without changing them.)

Classification of real processes can be tricky. Complex changes can be broken down into many simpler steps. Some of the steps are chemical and others are physical, so the overall process can't cleanly be placed in either category. For example, boiling coffee involves chemical change (the delicate molecules that give coffee its flavor react with air and become new, bitter-tasting substances) and physical change (the water in the coffee is going from liquid to gaseous form).

Author: Fred Senese senese@antoine.frostburg.edu



General Chemistry Online! What is the difference between chemical and physical change?

Copyright © 1997-2010 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 02/15/10.URL: http://antoine.frostburg.edu/chem/senese/101/matter/faq/physical-chemical.shtml