Grey and White tin

1. Apr 20, 2005

physicsss

Based on thermodynamic data found in your textbook, calculate the temperature at which white tin will convert into grey tin.

I have no idea how to do this...what equation should I use?

2. Apr 20, 2005

pack_rat2

Ah, the "tin pest"... I don't know for sure how to do it, but I think you might have better luck in getting help if you ask the question in the materials engineering forum.

3. Apr 21, 2005

osskall

To me it sounds like one would need more than thermodynamic data. The phase might be metastable at certain temperatures, i.e. thermodynamically white tin should convert to grey tin, but the kinetics are not sufficient for the conversion.
Wow, I really wouldn't know how to tackle this one. Do notify us when you know more ;)

4. Apr 21, 2005

GCT

what's the reaction pertaining to this problem?

5. Apr 21, 2005

pack_rat2

Gray Sn is an allotrope of Sn which is more stable than white Sn at lower temperatures. Actually, at room temp, white Sn is slowly turning into gray, though the process is extremely slow. There's a case I read about involving a old pipe-organ in Germany, which had pipes made of Sn that crumbled (became gray Sn) during a very cold winter day. Also, pewter, which is an alloy of Sn, should be protected from low temperatures. "Mellor's Modern Inorganic Chemistry" has info on this so-called "tin pest."

6. Apr 22, 2005

GCT

Interesting. Well, one general way to solve this problem is to use Gibb's free energy, find the temperature at which the reaction is spontaneous, when free energy equals 0. Zero indicates no overall reaction, while anything below indicates an overall reaction. You can either find the net free energy by subtracting the free energy of the reactant from the product.

Although there may be a more mathematically elegant way to do this.

7. Apr 27, 2005

osskall

OK, if the formulation "will convert to grey tin" should be interpreted as over time, maybe not even within some millennia, but it will happen, then the procedure sounds right and you need only thermodynamical data.