Heat of Solution: Hot Packs

Daley, Henry O.

doi:10.1021/ed071p791

Cited by 2 publications

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“…Some curricula have been designed to help students make these connections by constructing knowledge, but future research is needed on instructional design to address the findings of this research. Several experiments and demonstrations related to the dissolution of ionic salts and temperature changes have been published in this Journal. − Although these demonstrations may afford students the opportunity to develop their understanding of how changes they observe with their senses are due to changes at the particulate level of molecules and ions, we suggest that instructors who use these or similar experiments carefully examine their assessments in light of our findings.…”

Section: Implications For Research and Teachingmentioning

confidence: 95%

Dissolving Salts in Water: Students’ Particulate Explanations of Temperature Changes

Abell

Bretz

2018

J. Chem. Educ.

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This study investigates how students account for a macroscopic temperature change during the dissolution of ionic salts through particulate level explanations. Semi-structured interviews were conducted with general chemistry, physical chemistry, and biophysical chemistry students. During the interviews, students conducted hands-on tasks that included the touching of beakers containing exothermic or endothermic dissolution processes. Data analysis resulted in categorizing students into groups based on their ideas about bond breaking, bond making, and energy changes. Students’ particulate understandings of the dissolving process did not appear to impact their explanations of the energy changes they observed. Only two students (one from general chemistry and one from biophysical chemistry) correctly described both the dissolving process and the macroscopic energy changes. No students invoked the concepts of potential energy, lattice energy, or enthalpy of hydration to explain their observations.

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Section: Implications For Research and Teachingmentioning

confidence: 95%

Dissolving Salts in Water: Students’ Particulate Explanations of Temperature Changes

Abell

Bretz

2018

J. Chem. Educ.

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“…Graphical analysis of the temperature versus time graph provides initial, final, and change in temperature. Similar to Daley’s heat pack formulation procedure , students repeat this process twice but use decreased volumes of water, 70 and 50 mL of water, respectively. For each of the three runs, students calculate the heat of CaCl 2 dissolution Δ H ° diss (in units of J g −1 ) from the series of equations: q water = − q diss − false( m c normalΔ T false) water = q diss normalΔ H ° diss = q diss / m CaCl 2 Assumptions for this calculation are (i) calorimeter is perfectly insulating, (ii) all heat generated by the dissolution process is absorbed by the water, (iii) solution’s specific heat is equal to that of pure water, 4.18 J g −1 °C −1 , and (iv) Δ H ° diss is relatively constant over the temperature range of the experiment.…”

Section: Experiments Descriptionmentioning

confidence: 99%

“…Consequently, calorimetry experiments, which serve to enhance comprehension of thermochemistry, are included in the laboratory portion of the course . Moreover, a literature survey of “calorimetry” resulted in 20 publications detailing experiments to determine heat changes accompanying (i) acid−base neutralization , (ii) dissolution of solid and gas in aqueous solution − , (iii) changes of state − , and (iv) chemical reactions, for example, decomposition and combustion . Calorimetry experiments to determine specific heats were also found in the literature , .…”

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confidence: 99%

Thermochemistry to the Rescue: A Novel Calorimetry Experiment for General Chemistry

2010

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A novel calorimetry experiment that (i) provides “real-world” connections, (ii) assists students in learning thermochemistry, and (iii) uses equipment commonly found in an undergraduate general chemistry laboratory was implemented at our institution. Ultimately, students design a custom heat pack to treat the frostbitten hand of an Alaskan pipeline maintenance worker. First, students measure and use the specific heat of Vienna sausage to approximate the hand’s specific heat. Students obtained a mean specific heat of 3.1 ± 0.5 J g−1 °C−1 for Vienna sausage, which compares favorably with generally accepted values for the human body’s specific heat. Second, students qualitatively determine heats of salt dissolution and identify a salt for their heat pack. Next, students quantitatively determine their chosen salt’s heat of dissolution. Finally, using the Vienna sausage’s specific heat, students estimate the heat required to raise the temperature of the hand from 15 °C (frostbite risk) to 37 °C, calculate the amount of salt and water needed for their heat pack, and fashion and test their heat pack. To gauge student perceptions toward this experiment, a survey was administered. Results indicate that the majority of students enjoyed this experiment (69.3%) and felt that the experiment had “real-world” connections (59.4%).

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Heat of Solution: Hot Packs

Abstract: Determining how much CaCl2 must be present in a hot pack to produce a temperature of 110-120 F when mixed with 100 mL of water.

Cited by 2 publications

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Dissolving Salts in Water: Students’ Particulate Explanations of Temperature Changes

Dissolving Salts in Water: Students’ Particulate Explanations of Temperature Changes

Thermochemistry to the Rescue: A Novel Calorimetry Experiment for General Chemistry

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