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In high altitudes, food preparation becomes a problem. As the pressure decreases, the cooking time doubles for every 1500 meters. Self-heating meals or Heater Meals are very convenient for specialized mountain climbing and other survival expeditions. These products require no additional fuel to heat them and assure each individual a hot meal. This technology was developed for military expeditions and space travel. MREs, Meals Ready to Eat, and FRH, flameless ration heaters, were first introduced during DESERT STORM, 1991, to provide hot military meals for US soldiers. Self -heating meals have a shelf life of 2 years and heat in approximately 15 minutes. |
Self-heating meals are composed of a tray of food sealed within a patented bag. This bag contains a water pouch and a special heater pad. The heater pad is composed of a supercorroding alloy made of magnesium and iron mixed with sodium chloride in a porous matrix. A string is attached to the water pouch, which when pulled, releases water onto the heater pad. The pad heats up as it reacts with the water. Steam and heat released during the reaction heat the meal in 10 to 15 minutes. Other products of the reaction include magnesium hydroxide and hydrogen. The overall reaction within the heater pad is as follows:
Mg (s) + 2 H2O (l) → Mg(OH)2 (s) + H2 (g)
This reactions does not normally occur according to the activity series, however in the presence of iron, magnesium will corrode or react with water generating heat. |
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meals can heat 300.0 g of water from 4.0 °C to 76.0 °C in 12
minutes. Determine the amount of heat energy gained by the water
and released by the heater pad.
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Use the following table of Thermodynamic values for problems
2-4.
| Substance | ΔH (kJ/mol) | S° (J/K·mol) | | Mg (s) | 0 | 32.68 | H2O (l) | -285.830 | 69.91 | | Mg(OH)2 (s) | -924.54 | 63.18 | | H2 (g) | 0 | 130.684 |
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Calculate the enthalpy of reaction for the reaction of a heater pad. |
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Calculate the entropy of the reaction and predict if the system
is becoming more ordered or disordered. |
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Calculate the free energy of the system at 25°C and explain
if the reaction is spontaneous or nonspontaneous. |
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Supercorroding Alloys
New Ration Heater Wins Award
National Academy Press, Not Eating Enough
Hot Pack Self Heating Meals
Quake Pro |
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