Question

5. Meals-ready-to-eat (MREs) are military meals that can be heated on a flameless heater. The heat is produced by the following reaction: Mg(s) + 2H2O(l) --> Mg(OH)2(s) + H2(g) Calculate the number of grams of Mg needed for this reaction to release enough energy to increase the temperature of 25 mL of water from 17 to 87 degrees Celcius.

Answer 1

You need to know the delta H for the reaction. That isn't listed in the problem but you can look it up.
How much heat do you need? That's
q = mass H2O x specific heat H2O x (Tfinal-Tintial)
You have the data to calculate q needed.

Then 24.3 g Mg x (q in kJ/delta H iin kJ) = g Mg needed.