# Energy released by aluminum reactions

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.

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

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:

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!!