JCE Classroom Activities are edited by Erica K. Jacobsen
Instructor Information
JCE Classroom Activity: #103
Enjoy a Hot Drink, Thanks to Chemistry!
Gabriel Pinto,1 Maria T. Oliver-Hoyo,2 and Juan Antonio Llorens-Molina3 1Universidad
Politécnica de Madrid, Spain;
[email protected]. 2Chemistry Department, North Carolina State University, Raleigh, NC 27695;
[email protected]. 3Universidad Politécnica de Valencia, Spain;
[email protected] In this Activity, students investigate the heat produced by the dissolution process of calcium chloride in water and use the information to design a self-heating beverage container. Self-heating or self-cooling containers for meals and beverages are excellent examples of chemistry in action in the everyday life of consumers. Such containers have dual chambers in which the food is usually contained in the internal chamber while the chemical process that would heat or cool the food or beverage occurs in the other (1). An example of these self-heating beverages are “autocalentables” that are commonly sold in European countries for ~1.50€ (~$2.00) and include different types of coffee (plain, with milk, or cappuccino), hot chocolate, and tea (2). In this Activity students investigate the chemistry that makes these products possible. Dissolution of a salt in water is often accompanied by a temperature change: if the temperature increases, the solution process is exothermic and if the temperature decreases, the process is endothermic. This Activity takes advantage of the exothermic process that occurs when calcium chloride dissolves in water, as in the “autocalentables”.
Integrating the Activity into Your Curriculum This Activity illustrates concepts such as enthalpy of solution, enthalpy of reactions, heat transfer, and stoichiometry. This Activity can connect a variety of chemistry topics and provides the opportunity to practice commonly needed operations, such as unit conversion and algorithmic problem solving with a purpose. It can be used with high school students as well as in an introductory college course. This Activity can be extended using an article published in this issue of JCE (1) that includes information on self-heating beverages and MREs—meals ready to eat.
About the Activity
This Activity is simple to prepare and perform. Anhydrous calcium chloride (granulated) is available in hardware stores as a de-icer and in discount and grocery stores as a product for dehumidification. The solutions can be washed down the drain with copious amounts of water. The dissolution process from a variety of salts could also be considered and used to target the desired temperature changes (3). Although the chemistry is the crucial element that makes self-heating containers possible, it alone does not make these products work. Students will need to reflect on their chemical data and calculations and add to it in order to propose the design of an effective self-heating container. The figure on the Student Activity shows a cutaway diagram of self-heating containers commonly found in Europe. See the online supplement for the same figure, with labels.
perforated
Answers to Questions
1. The process involved is a dissolution process where CaCl2(s) → Ca2+(aq) + 2Cl−(aq). 2. Students should find the value for the dissolution enthalpy of CaCl2 in water (ΔHdissolution = −82.9 kJ/mol). The heat liberated would be: −82.9 kJ/mol × (5.0 g CaCl2 / 111.0 g/mol) = −3.7 kJ. It is an exothermic process. 3. Container masses and materials will vary. Using Q = mcΔT, −3.7 kJ = [(mass of outer water/salt + mass of simulated beverage)(specific heat of water)(ΔT )] + [(mass of outer container + mass of inner container)(specific heat of the containers’ material, if the same)(ΔT )]. 4. A typical result in testing using plastic cups was an increase in temperature of 14 °C (from 25 to 39 ºC). 5. The simulated beverage will likely reach a temperature considerably less than calculated. Factors related to this include assuming that: (i) the salt solution had the same specific heat as water; (ii) the system is perfectly isolated from the environment; and (iii) enthalpies do not vary with temperature changes. These considerations may prompt discussion of which materials would work best for containers, what quantities of salts would be more practical, and which salts provide greater changes in temperature, among others. 6. The desired temperature depends on the consumer’s preference; however, 70–80 ºC are typical temperatures for hot beverages. Typical volumes for these beverages are 75 mL (2.5 fl. oz.), 119 ml (4 fl. oz.), or 238 ml (8 fl. oz.). 7. Design considerations could include: salt amounts and properties; cost and hazards considerations; using environmentally sustainable materials; and container properties, such as an insulating outer container and a conductive inner container. 8. Salts with an endothermic dissolution process could be used to cool a beverage. Ammonium nitrate, NH4NO3, is a salt commonly used for this. Iced tea and cold coffee beverages are advertised (4) with information about the cooling process by means of the dissolution of sodium thiosulfate, Na2S2O3 · 5H2O, in water. In this case the ΔHdissolution = +47.4 kJ/mol.
References, Additional Related Activities, and Demonstrations
This Classroom Activity may be reproduced for use in the subscriber’s classroom.
fold here and tear out
Background
(accessed Sep 2009)
1. Oliver-Hoyo, M. T.; Pinto, G.; Llorens-Molina, J. A. The Chemistry of Self-Heating Food Products: An Activity for Classroom Engagement. J. Chem. Educ. 2009, 86, 1277–1280. 2. Self-heating beverage information: http://www.confitelia.com/ (Click on one of two flags on the right-hand side of the menu bar to toggle between the Spanish or English version. Then click “bebida autocalentable” or “self-heating drink”.) 3. Silberman, R. G. Some Like It Hot, Some Like It Cold. J. Chem. Educ. 2004, 81, 64A–64B. 4. Information about self-cooling beverages: http://www.caldocaldo.it/freddo/eng/index.html. Supporting JCE Online Material at http://www.jce.divched.org/Journal/Issues/2009/Nov/abs1280A.html
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 86 No. 11 November 2009 • Journal of Chemical Education
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JCE Classroom Activity: #103
Student Activity
Enjoy a Hot Drink, Thanks to Chemistry! Consumer products known as self-heating foods or beverages are available that enable you to heat the food or drink contents using a chemical reaction or solution process of a salt in water. (See Figure 1.) This chemistry in action has been used since the 1900s when mountaineers and explorers recorded the use of self-heating cans in their travels. British troops had these self-heating cans in their food rations during World War II and now military personnel and outdoors enthusiasts commonly use these products. A variety of these beverages, including coffee, hot chocolate, and tea, are found at gas stations, airports, and highway rest stops in European countries. In this Activity, your challenge is to investigate the heat of dissolution of calcium chloride and use the information to design your own self-heating beverage container. You must think about how such a container works: how could chemistry be used to heat the beverage? How can the process and the beverage remain separate? How can it be heated when you are ready to drink and not before?
Try This You will need: granulated anhydrous calcium chloride (used for de-icing or dehumidification), water, thermometer, balance, stir rod or spoon, and two differently sized containers (the inner container should fit loosely inside the outer container). __1. Investigate what the desired temperature of a beverage such as coffee or hot chocolate should be. Poll your classmates to determine at what temperature most people enjoy their hot beverage. You could also measure the temperature of a hot beverage from a cafeteria. __2. Determine the volume of an average single-serve hot beverage in mL. __3. Place 10.0 g of room-temperature water into the selected larger outer container. Measure and record its initial temperature. Figure 1. A schematic drawing of __4. Place 6.0 g of room-temperature water into the selected smaller inner container. self-heating containers commonly This serves as a simulated beverage. Measure and record its initial temperature. found in Europe. __5. Add 5.0 g of granulated anhydrous calcium chloride to the water in the larger outer container and quickly stir to dissolve the salt. Immediately place the smaller inner container inside the larger outer container, so the inner container nests inside the outer container. The inner container will be sitting in the solution of dissolved salt. __6. Observe how the temperature of the simulated beverage in the inner container changes. Record the highest temperature the simulated beverage reaches.
Questions 1. Write the chemical equation that describes the process involved in heating the beverage. 2. Calculate the heat (in kJ) liberated during the dissolution of CaCl2 in the larger outer container of water in step 5. Is this an exothermic or an endothermic process? Be Safe! 3. Calculate the theoretical temperature change for the simulated beverage in the smaller Calcium chloride may cause severe irriinner container, based on the liberated heat calculated in Question 2. The process tation, even burns, if it comes in contact is related to the equation Q = mcΔT in which the mass of the system (m) receives with moist skin. You may use gloves to energy as heat (Q), resulting in a temperature change (ΔT ). The specific heat (c) and avoid skin contact, but if contact occurs masses of each piece of the system need to be taken into consideration, including the flush the affected area with plenty of two containers, the simulated beverage, and the solution in the outer container. water. Keep the solid in a tightly closed 4. What temperature did your simulated beverage reach? container as it will absorb water from 5. Does the theoretical temperature calculated in Question 3 match the observed temthe atmosphere. perature from Question 4? Provide explanations and state possible assumptions. 6. What did you decide the amount of the beverage would be? What temperature did you decide would be the desired temperature? 7. Propose a design for a self-heating beverage container. Scale up the design for the desired temperature change and beverage size you answered in Question 6. 8. Propose a chemical process that could be used to cool a beverage rather than to heat it.
Information from the World Wide Web (accessed Sep 2009) 1. Self-heating beverages: (a) http://www.caldocaldo.it/eng/index.html. (b) http://www.calientecaliente.es/. (This Web site is in Spanish—even if you do not know Spanish, click the tab El Vaso Autocalentable to see a video demonstration.) 2. History and operation of self-heating containers: http://en.wikipedia.org/wiki/Self-heating_can. 3. How MREs (Meals Ready to Eat) work: http://science.howstuffworks.com/mre.htm. This Classroom Activity may be reproduced for use in the subscriber’s classroom.
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Journal of Chemical Education • Vol. 86 No. 11 November 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
