Why is the oxidation of aluminum metal by hydrochloric acid exothermic?

Answer 1

Because you are making strong #Al-Cl# and #H-H# bonds, i.e.

#Al(s) + 3HCl(aq) rarr AlCl_3(aq) + 3/2H_2(g)#

For these issues, it's important to memorize the following mantra:

#"bond breaking requires energy and bond making releases energy".# The energy released or consumed by a chemical reaction is always the balance between bonds broken and bonds made.
When aluminum metal is oxidized by hydrochloric acid we break reasonably strong #Al-Al# bonds. We make STRONGER #H-H# and #Al-Cl# bonds, (Of course the aluminum chloride is solvated in water, bond formation takes places nonetheless.) Capisce?
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Answer 2

The oxidation of aluminum metal by hydrochloric acid is exothermic because it involves the release of energy as heat. This reaction releases energy because the products formed have lower potential energy than the reactants.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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