Passage VI

Flameless ration heaters (FRHs) are used by combat soldiers to heat their meals in the field. The heat is produced when magnesium reacts with water:

Mg(s) + 2H₂O(l) → Mg(OH)₂(s) + H₂(g) + heat

The rate of the reaction increases in the presence of iron (Fe) and sodium chloride (NaCl). The following experiments were done to determine how to design FRHs.

Experiment 1

A 1.0-mole (mol) piece of Mg ribbon, 0.10 mol of Fe powder, and 0.10 mol of NaCl were added to 25 mL of H₂O at 20°C in an insulated container. The mixture was stirred constantly and its temperature was measured every 50 sec. The experiment was repeated with Mg ribbon cut into 100 pieces and with Mg powder (see Figure 1).

Experiment 2

Powdered Mg (0.10 mol) was mixed with 0.10 mol of NaCl. The mixture was added to 100 mL of H₂O at 20°C in an insulated container. The mixture was stirred constantly and the maximum temperature increase that occurred within 15 min was recorded. The procedure was repeated with different amounts of Fe powder added to each mixture (see Table 1).

Experiment 3

Powdered Mg (0.10 mol) was mixed with 0.50 mol of Fe powder and added to 100 mL of H₂O at 20°C in an insulated container. The mixture was stirred constantly and the maximum temperature increase that occurred within 15 min was recorded. The procedure was repeated with different amounts of NaCl (see Table 2).