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I heard that aluminum reacts violently when exposed to hydrochloric acid. I was wondering how much energy is released by this reaction. Preferably in MJ/kg or MJ/l. Assuming the reaction needs 2 moles of aluminum for every 6 moles of hydrochloric acid.

$$\ce{2Al(s) +6HCl(aq)→2AlCl3(aq) +3H2}$$

There is also another reaction which mixes aluminum with sodium hydroxide. How much energy is released by this reaction (MJ/kg or MJ/l)? Assuming 1 mole of aluminum is mixed with 1 mole of sodium hydroxide.

$$\ce{2 Al(s) + 2 NaOH(aq) + 2 H2O(l) → 2 NaAlO2(aq) + 3 H2(g)}$$

I've found notes on the energy density of each substance; however, I do not know the efficiency of these reactions or the total energy released.

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    $\begingroup$ You'd want serious excess of acid/base to completely dissolve Al. Also these reactions aren't exactly violent in comparison with explosives. $\endgroup$
    – Mithoron
    Apr 21 at 22:00
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    $\begingroup$ Why not calculate them from enthalpies from some data table? $\endgroup$
    – Mithoron
    Apr 21 at 22:01
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    $\begingroup$ I calculated the enthalpies; however doesn't this assume 100% efficiency? $\endgroup$
    – Nitrogen-8
    Apr 22 at 12:23
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    $\begingroup$ What is for you the "efficiency" of this reaction ? The yield ? $\endgroup$
    – Maurice
    Apr 22 at 16:26
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    $\begingroup$ The quantity of energy that can be converted into mechanical energy. $\endgroup$
    – Nitrogen-8
    Apr 22 at 19:01

1 Answer 1

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I tried making an attempt. I mainly used ΔH values that i found online for these equations.

  1. Aluminum and Hydrochloric Acid:

ΔH = -1049 kJ/mol (Taken from this source: https://www.wyzant.com/resources/answers/833716/calculate-the-h-for-the-reaction-2-al-s-3-cl2-g-2alcl3-s-from-the-following)

Convert ΔH from kJ/mol to MJ/mol: ΔH = -1049 kJ/mol x (1 MJ / 1000 kJ) = -1.049 MJ/mol

Molar mass of Aluminum (Al) = 26.98 g/mol

Energy released per kilogram of Aluminum (MJ/kg):

Energy per kg Al = ΔH / (molar mass of Al) x (1000 g/kg)

Energy per kg Al = -1.049 MJ/mol / (26.98 g/mol) x (1000 g/kg)

Energy per kg Al ≈ -38.9 MJ/kg

  1. Aluminum and Sodium Hydroxide:

ΔH = -346.2 kJ/mol (Taken from this source: https://www.quora.com/How-would-you-answer-this-equation-Standard-enthalpy-change-for-the-reaction-to-be-346-2-kJ-2Na-s-2-H2O-l-2NaOH-aq-H2-g-The-standard-enthalpy-of-formation-of-H2O-l-is-kJ-mol)

Convert ΔH from kJ/mol to MJ/mol: ΔH = -346.2 kJ/mol x (1 MJ / 1000 kJ) = -0.3462 MJ/mol

Molar mass of Aluminum (Al) = 26.98 g/mol

Energy released per kilogram of Aluminum (MJ/kg):

Energy per kg Al = ΔH / (molar mass of Al) x (1000 g/kg)

Energy per kg Al = -0.3462 MJ/mol / (26.98 g/mol) x (1000 g/kg)

Energy per kg Al ≈ -12.8 MJ/kg

hope this helps!!

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