Sciencemadness Discussion Board

Activation Energy and Heat

MttLsp - 15-7-2010 at 19:14

I'm new to chemistry. I am trying to make some Stannous Chloride (SnCl2) from lead free solder wire (95% Tin, 5% Antimony) and Muriatic Acid. I used stoiciometric amounts. The antimony does not react with the HCl at room temperature, but the Tin does:
Sn + 2HCl --> SnCl2 + H2 (g)
The problem is that the reaction is incredibly slow; the boiling flask has been sitting for over a week and hydrogen is still bubbling out, slowly but surely. I thought about adding heat as a catalyst, but I am afraid the antimony will react if I add to much and give me an impure product. More importantly, I don't want my basement filling up with poisonous gas and HCl. Does anyone know how to calculate the temperature needed to carry out a given reaction?

gsd - 15-7-2010 at 21:23


I wonder if such universal all encompassing correlation can ever be found, given the complexity and diversity of the problem.

However for your purpose the Arrhenius equation is quite sufficient.
Roughly speaking, it can be concluded from it that the rate of reaction (for any reaction) doubles every 10 Deg C rise in the reaction temperature.

http://en.wikipedia.org/wiki/Arrhenius_equation

So say if Sn is getting dissolved in HCl at a rate of 1 gm/hr at 30 Deg C, then at 100 Deg C the rate of dissolution will be 128 gm /hr.

There is no way you can avoid the heating in your experiment. You will have to tackle the problem of removing the Antimony by chemical methods after both Sn and Sb are gone into the solution.

gsd

zed - 15-7-2010 at 22:08

Anodize it. Hook it up to a battery charger or some other DC power supply. Yup, even one those cheezy little square black 2inchx2inch suckers will probably do the trick.

Expecting that the Antimony will somehow not go into solution.....Well, I wouldn't count on that.

Might be easier to start with Tin Oxide. The local rock shop, or lapidary club, might sell you a small portion cheap. Folks use it for polishing stones.

peach - 3-8-2010 at 15:34

Thanks for the reminder of the equation GSD. I was reading that article a while ago and then forgot the name of it. I found the following particularly interesting;
Quote:
Given the small temperature range kinetic studies occur in, it is reasonable to approximate the activation energy as being independent of the temperature. Similarly, under a wide range of practical conditions, the weak temperature dependence of the pre-exponential factor is negligible compared to the temperature dependence of the \scriptstyle \exp(-E_a/RT) factor; except in the case of "barrierless" diffusion-limited reactions, in which case the pre-exponential factor is dominant and is directly observable.