Even though I am using a question from my homework, I would greatly appreciate the process of how to determine "the enthalpy change", more so than the actual answer.

"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...

"What quantity of magnesium is needed to supply the heat required to warm 17 mL of water (d = 1.00 g/mL) from 28°C to 82°C?"

But that is solved by "(mL of water)x(density of water/1mL of water)", correct?


Thank you for your time~

You need more information, namely, the amount of energy needed to break the Mg and H2O bonds, and the energy released when Mg(OH)2 and H2 bonds are formed.

With these, you should be able to work out the enthalpy change in the reaction.

For the second part, the question goes a little into Physics, where the formula Q=m x c x(delta theta) is used. Q is quantity of heat, m is mass, c is specific heat Capacity and delta theta is the change in temperature.

So, Q will be mass of water in kilograms, which you get by

But that is solved by "(mL of water)x(density of water/1mL of water)", correct?

and converted into kilograms, multiplied by 4200J/(kgK) (specific heat capacity of water) and 54 K (obtained by 82 Celsius - 28 celcius).

You will obtain the energy required, and I think that you will be able to continue, since you know how much energy the reaction of magnesium and water produced, and the amount of energy you need?