Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Water at 4 Degrees Celsius
Name: fehmi
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: 1999-2001


Question:
Why is water's volume smallest at 4 Celsius?


Replies:
fehmi,

At temperatures above absolute zero (0 K, -273 C), all molecules are in incessant random motion. Such movements rather interfere with their ability to hold on to each other. For example, at the boiling point of water (100 C) the molecules are able to tear away from each other and move from a liquid phase into the gaseous phase that you recognize as vapor.

As the temperature of liquid water is reduced, random movements of the water molecules are likewise reduced. At 4 C, molecular motion has been diminished to the point where the hydrogen bonds that held them together in the liquid phase are beginning to settle into an optimum (best) arrangement that will ultimately bind them together in the ice latticework at 0 C. From about 4 C to water's freezing point at 0 C, the molecules are no longer able to so easily slip past each other as they did in the liquid phase. They begin to really "feel" the intermolecular attraction of hydrogen bonding which occurs between the hydrogen atoms of one water molecule and the oxygen atoms of nearby molecules. Thus, they begin to take on an orderly crystalline arrangement that we recognize as ice. The ice latticework simply takes up more space than the slightly more compact and disordered liquid state. Water expands when it freezes.

Water is unusual in this regard. Most substances shrink when they pass from the liquid to solid state.

Check introductory chemistry textbooks under the heading of "hydrogen bond" for a more detailed explanation.

Regards,
ProfHoff



Click here to return to the General Topics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory