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 NSF Cooperative Agreement No. DUE 9255745 Copyright, 1994, Maryland Collaborative for Teacher Preparation Student handout ---------------------------------------------------------------------- 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.