MCTP
Maryland Collaborative 
for Teacher Preparation
 
 
Water, water, everywhere...."
 
 
Thomas C. O'Haver
Department of Chemistry and Biochemistry
University of Maryland
College Park, MD 20742
(301) 4051831
to2@umail.umd.edu
 
 
NSF Cooperative Agreement No. DUE 9255745
 
Copyright, 1994, Maryland Collaborative for Teacher Preparation
 
Student handout
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Chemistry 121/122                    Name_________________________________
 
Chapter 5 Class Work                 Partner ______________________________
 
                 "Water, water, everywhere...."
 
This is not a quiz, but rather a class exercise.  The papers will be
collected and graded.  You may talk to your classmates and you may refer to
your textbook, but you must write your answers to each question in your own
words.  (Don't just copy things right out of the textbook).
 
1. The energy required to decompose water vapor into hydrogen and oxygen
gas
 
                  2H O (g) -->  2H  (g) + O (g)
                    2             2        2
 
is approximately 480 KJoules/mole.  The (g) means that the material is in
the gas phase.  The textbook* gives the heat of vaporization of water
 
                      H O (l)  -->  H O (g)
                       2             2
 
as 9720 cal/mole (page 140*).   The (l) means that the material is in the
liquid phase.
 
  a. Which is greater, the energy required to decompose a mole of water or
  the energy required to vaporize a mole of water?  1 cal = 4.182 Joules.
 
  b. What kind of bonds exist between water molecules in liquid water?
 
  c. Compare the kind and strength of the bonds which are broken when water
  is decomposed and when it is vaporized.
 
2.  In what ways is water not typical of other simple molecules of about
the same size and molecular weight?
 
3.  Briefly describe three different ways that salt can be removed from
salt water to make drinkable fresh water.  Which of these ways are actually
used in practice?
 
4.  a. Suppose you want to make some hot tea, but all you have is a
coal-burning stove.  How many grams of coal (p. 103) would you have to burn
in order to produce enough heat energy to heat one liter (1000 grams) of
water from room temperature (20 degrees C) to its boiling temperature?
(Hint: p. 138*).  b. What practical realities might make this amount of coal
inadequate to the task in a real stove?
 
 
* American Chemical Society, "Chemistry in Context: Applying
Chemistry to Society", Wm. C. Brown Publishers, 1994.