Simple Heat Flow Measurements A Closer Look at Polystyrene Cup Calorimeters Lawrence N. Ngeh, John D. Orbell, and Stephen W. ~lgger' Department of Environmental Management, Victoria University of Technology, St. Albans Campus, McKechnie Street, St. Albans, 3021, Australia
The educational literature contains many papers relating to the construction andlor use of calorimeters for teaching purposes. Examples of these include an isobaric calorimeter for determining the calorific content of simple foodstuffs (I), a n isothermal calorimeter for measuring heats of vaporization (21, a differential microcalorimeter for studying reaction enthalpies in solution (31, a low-cost labyrinth calorimeter (41,and various other calorimeters that have been designed for studying reactions in solution (5-7). Furthermore, a most elegant paper describing both the theoretical derivation of the heat capacity of metals and a calorimetric ex~erimentto measure this quantitv has appeared in the educational literature (8,. More recentlv, the use of -polvstyrrne foam cups as "calo- rimeters" in ;hdergraduate teaching laboritories has proven to be a most economical and convenient means by which to introduce students to elementary thermochemical measurements. Many modern textbooks (9-11) and laboratory manuals (12,13) describe experiments in which, typically, a polystyrene cup is used as a calorimeter to measure the heat capacity of a metal or the enthalpy change associated with a chemical process. A few experiments that involve the construction and use of polystyrene cup calorimeters in undergraduate teaching also are described in the mainstream educational literature. These include the measurement of the heat of sublimation of dry ~olvstvrene microice (14) and the construction and use of . - calorimeters (15). To our knowledge, despite the significant number of papers in the educational literature devoted to calorimetry, the elementary topic of heat flow and the simple calculations relating to it have yet to be addressed formally. This article describes a sequence of experiments based on the use of polystyrene cup calorimetery together with simple computer programming that we have found to be most effective in illustrating the principles of heat flow to junior undergraduate students. The Apparatus The experiments are performed using as "calorimeters", 200-mL polystyrene drinking cups that can be obtained readily from any supermarket; mercury-in-glass thermometers (0-110 f 0.1 "C, -10-50 f 0.05 "C ; a hotplate I
Author to whom correspondence should be addressed.
suitable for heating a 400-mL beaker containing about 200 mL of water: a maenetic stirrer and "flea" to stir the con., tents of the cnlonmeter; a ceramlc electric jug I 1-L capacity,; a digital multimatcr (Escort, model EDM-1631. The Experiments
Simple Calculations Relating to-HeatFlow The original idea that heat is a measurable quantity that mav flow from one bodv to another has been attributed (16) to
