What chemical similarities are there between reactions of elements with water and reactions of elements with acid?

 

How would you explain the difference in reactivity between an element in water and an element in acid?

I can think of some things that are not similar between rxn's of a substance with water and rxn of a substance with an acid. Can you be more specific as to what you're looking for?

More specifically, the elements are Mg, Ca, S, and Al with HCl.

 

If that doesn't help then nevermind, I think I'm starting to figure it out.

More specifically, the elements are Mg, Ca, S, and Al with HCl.

 

If that doesn't help then nevermind, I think I'm starting to figure it out.

 

Well, reactions will occur between HCl and Mg, Ca, and Al because these metals have a stronger activity than hydrogen. As for sulfur, a non-metal, it has 6 valence electrons, so it will need 2 hydrogens to fill its octet. I hope that helps, but I'm not sure what you're asking in regard to rxn's with water.

Basically, there is not a real difference in the nature of the reactions. Water also acts as acid, due to self-ionization.

 

In practice, however, the difference is large. The type of reaction is very similar, but in acid the reaction proceeds at a MUCH higher rate, certainly for Mg, Al. If the water is heated, then also Mg dissolves at an appreciable rate in water, Al only reacts when very finely divided and with temperatures of several hundreds of C.

 

The element S is a different story. It does not react with HCl, nor with H2O. This does not show a displacement reaction and no S(n+) ions are formed.