[orgo814]

I'm supposed to predict products based on the activity of the metals (pauling electronegativity). Please tell me if I'm right.

1) Cu + AuCl -->
Cu has electroneg of 1.90 while Au has electroneg of 2.54 (very inactive). Since Au is considered slightly electropositive, I assumed the reaction would ago and a displacement would occur producing CuCl2 and Au (Cu is oxidized, Au reduced)

2. La + H2O -->
Since La is very electropositive it will react with water and release hydrogen gas but I'm unsure of what the first product would be. I guessed it to be La(OH)3 + H2 (wasn't sure if a hydroxide would form or not)

3. Au + HBr -->
Since Au has such low activity with its high 2.54 electronegativity, there should be no reaction since it is incapable of being oxidized by acid

4. Ti + HCl --> TiCl4 + H2
Since Ti has electronegativity of 1.54, it is likely going to be oxidized by acid

5. Be + H2O -->
Since Be is electropositive (but not that electropositive) it shouldn't react with water. My book states that electronegativity value needs to be below 1.4 for that to happen. Therefore no reaction

6. U + HCl -->
U is very electropositive with its 1.38 electronegativity therefore it will be oxidized by acid. My predicted products were UCl6 + H2

7. Pt + Hg(NO3)2 -->
Since Hg is a more active metal than Pt, it is likely going to oxidize Pt and there would be a displacement reaction. Products= Pt(NO3)4 + Hg

[Hunter2]

1 yes, 2 probably oxidlayer like aluminium, 3. no, 4. no 5 yes,6 no, 7. no

[Enthalpy]

http://www.webelements.com/lanthanum/
click more elements for other reactions.

I dislike the idea of metal reactions determined by the electropositivity. Stable oxide layers are just as important, as we see everyday with aluminium, zinc, stainless steel, titanium...

Also, every single detail of alloying makes a huge difference in the corrosion resistance, as well as the alloy's heat treatment. One example: if Cr18-Ni10 stainless steel must resist rain after being welded, then we demand <0.02%C in the alloy instead of <0.06%C (because Cr-C precipitation would deplete superficial Cr at the seam, they say). Other example: in sea water, 2% Mo in Cr17-Ni12 stainless steel prevent corrosion by chlorides - good luck to explain this through electropositivity. Same gags with aluminium.

[ajkoer]

Enthalpy argument is in line with the discussion in Wikipedia on Reactivity series (see http://en.wikipedia.org/wiki/Reactivity_series ).

Basically, the Reactivity series is based on

1. Reaction with water and acids
2. Single displacement reactions
3. Comparison with standard electrode potentials.

Clearly, passivation as a result of oxide layers and alloys impacts "Reaction with water and acids".

Now, with respect to "Single displacement reactions", Wiki notes, to quote:

"other factors can come into play, such as in the preparation of metallic potassium by the reduction of potassium chloride with sodium at 850 °C. Although sodium is lower than potassium in the reactivity series, the reaction can proceed because potassium is more volatile, and is distilled off from the mixture.

 Na (g) + KCl (l) → K (g) + NaCl (l) "