applications anJ analoqiss Storing Solar Energy in Calcium Chloride
Cachran, GA31014
Step 1. Heating calcium chloride hexahydrate from 20.0 'C (68.0 'F) to 30.0 'C (86.0 'F). Heat energy = (change in temperature)(mass)(~peeific heat) Heat energy = (10.0 W219.08 g/mo1)(1.34Jlg 'CX1 moll = 2,940 J (3)
Curtis C. Wilkins, Norman W. Hunter, and Earl F. Pearson Western Kentucky University Bowling Green, KY 42101
One can help students to relate their study of chemistry to the world around them by examining the question of whether i t is feasible to store solar energy in calcium chloride hexahydrate (or in a hydrated salt). Such a n application of thermochemical concepts to "real-life" is greatly appreciated by students. Some of t h e same concepts considered in this application (including some other possible solar energy storage media) have been described aptly by Spears ( I ) and by Fouda (2). To arrive a t a determination of the feasibility of storing solar energy in a hydrated salt one must employ chemistry concepts and energy concepts and then make decisions regarding reasonable approximations. The energy concepts and chemistry concepts and decision making involved in answering the feasibility question include the following: Energy Concepts ,,tion = =formation, pmducts Nreactian = - AHreveras reaction
edited by
RON DELORENZO Middle Georgia College
formation, resetenfs
Heat of vaporization Heat flaw = (AT)(speeifieheat)(mass) Specific heatheat capacity Law of Additivity of Heats
Chemistry Concepts
Mole concept (interconvertingglmoles) Stoichiometric relationships (both masslenergy) Determination of what reaction(s)may (or may not) occur
Step 2. Convetimg the hexahydrate (at 30.0 'C) to the dihydrate and water
Heat energy = (-1402.90 kJ/mol)(lmoll + (-285.85 kJlmolX4 moll - (-2607.89 kJ/mol)(lmoll = +61.59 kJ ( 4 ) Total energy stored = 2.94 kJ + 61.59 kJ = 64.53 kJ A typical eight-room house requires 200,000 BTU or 211,000 kJ (per day). Therefore, to store an adequate amount of solar energy for an eight-room house would require 3.270 mol (716 k e or 1580 lb) of calcium chloride
