Homework Help: chem

Posted by Anonymous on Saturday, November 20, 2010 at 11:17pm.

I got through the first part easily, got -352.9kJ
Having trouble with the second part

"The meals-ready-to-eat (MREs) in the military can be heated on a flameless heater. The source of energy in the heater is shown below.

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

Calculate the enthalpy change under standard conditions, in joules, for this reaction."

The second part of this problem is....

How many grams of Mg are needed to raise the temperature of 25.0ml of water from 25.0 C to 85.0 C

chem - DrBob222, Sunday, November 21, 2010 at 12:27am
Energy needed is q.
q = mass H2O x specific heat water x (Tfinal-Tinitial). Then

g Mg = 24.3 x (q kJ/352.9 kJ)

Check my thinking.

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