### Re: Do any chemicals get cold when they come into contact with electricity?

Date: Mon Nov 14 15:40:43 2005
Posted By: Elizabeth DeBartolo, Faculty, Mechanical Engineering, Rochester Institute of Technology
Area of science: Chemistry
ID: 1131349842.Ch
Message:

Well, I'm a mechanical engineer answering an electricity question, but I'll do the best that I can! :)

First, the basics...
Materials are made up of atoms - in a conductor, those atoms are arranged in a sort of 3-dimensional grid called a lattice. If the temperature is above absolute zero, those atoms have some nominal energy level that makes them vibrate in place. The free electrons in the material also move around.

When a current is passed through a conducting material, the electric field increases the kinetic energy of the electrons, causing them to move around more. They bounce off of neighboring atoms or ions and eventually slow back down - the kinetic energy is transferred into thermal energy due to the collisions. This is what makes materials heat up when a current is passed through them. The amount of power dissipated can be calculated in one of the following ways:
P=IV
P=(I^2)R or
P=(V^2)/R

In each case, P is the power, I is the current, V is the voltage, and R is the resistance of the material. The static resistance is alwasy positive, so in each of these equations, the voltage or current can be either positive or negative, but they will be positive or negative together. So the product "IV" is always positive (either +# times +# or - # times -#). In the other two equations above, the current or voltage is squared, and squaring either a positive or negative number gives a positive. So far, it sounds like heat is always generated (P is positive). The heat generated is just power X time, so as long as time is positive, (tough to change!) you're always generating heat and the material won't cool off.

In researching the answer to your question, I came across some references to materials with zero or negative static resistance, but it seems that this is still somewhat controversial. A scientist at SUNY-Buffalo has published a journal paper on the topic. The paper doesn't mention anything about the material actually cooling off, so I still don't know if this would be an example of cooling materials by passing electricity through them.

I hope this at least points you in the right direction!

Beth DeBartolo

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