Calculate the number of grams of Mg for this reaction to release enough energy to increase the temp of 71 mL of water from 22 ∘C to 79 ∘C.?
Update:
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).
Part A
Calculate the standard enthalpy change for this reaction.
Express your answer using four significant figures.
ΔH∘rxn =
-353.0
kJ
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Answers & Comments
Yes
First, calculate the heat required:
q = m c (T2-T1)
q = 71 g (4.184 J/gC) (79-22 C) = 1.69X10^4 J
Now, the enthalpy of the reaction tells you that 1 mol of Mg will release -353 kJ of heat. So:
16.9 kJ X (1 mol / 353 kJ) = 0.0480 mol Mg
Mass Mg = 0.0480 mol X 24.3 g/mol = 1.17 grams Mg