The meals-ready-to-eat (MREs) in the military can be heated on a flameless heater. You can purchase a similar product called “Heater Meals”.  Just pour water into the heater unit, wait a few minutes, and you have a hot meal. The source of energy in the heater is the exothermic reaction of magnesium with water:                                        Mg(s) + 2 H2O(ℓ) → Mg(OH)2(s) + H2(g)                                                                ΔHf° (kJ/mol)                        Mg(s)                                0                        Mg(OH)2(s)             –924.5                        H2O(ℓ)                       –285.8                        H2(g)                                 0          Calculate the mass, in g, of magnesium needed to supply the energy required to warm 25.0 mL of water from 25.0 °C to 85.0 °C. The density of water is 1.00 g/mL, and its specific heat capacity is 4.184 J/g∙°C. 0.432 g 0.126 g 1.244 g 2.740 g 0.745 g

Question

The meals-ready-to-eat (MREs) in the military can be heated on a flameless heater. You can purchase a similar product called “Heater Meals”.  Just pour water into the heater unit, wait a few minutes, and you have a hot meal. The source of energy in the heater is the exothermic reaction of magnesium with water:

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

                                                               ΔHf° (kJ/mol)

                       Mg(s)                                0

                       Mg(OH)2(s)             –924.5

                       H2O(ℓ)                       –285.8

                       H2(g)                                 0         

Calculate the mass, in g, of magnesium needed to supply the energy required to warm 25.0 mL of water from 25.0 °C to 85.0 °C. The density of water is 1.00 g/mL, and its specific heat capacity is 4.184 J/g∙°C.

0.432 g

0.126 g

1.244 g

2.740 g

0.745 g

 

 

 

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