Re: Does a solution of car antifreeze and water cool better then water

Sorry about your back pain and your desire to freeze the pain away.  
Antifreeze, however, is not your answer.  

We use ice to maintain cold temperatures because of the heat adsorbed when 
the ice melts into water.  It takes quite a bit of energy to get the water 
molecules to leave their solid state and get them moving around in liquid 
form.  Specifically, it takes about 80 calories per gram of water  (a 
calorie and an BTU are both units of heat; they just differ in size).  This 
energy is called the latent heat of fusion, so sometimes simply the heat of 
fusion.

In addition to adsorbing energy as the ice melts, the ice water also 
adsorbs energy as it heats from 0 C to whatever temperature is too warm to 
do your back any good.  The specific heat of water is quite high, compared 
to most materials; it is about 1 calorie per degree per gram of water.  So, 
if the melted ice water heats from 0 to about 20 degrees C(barely below 
room temperature) it will adsorb an additional 20 calories from your aching 
back.  So, the majority of the cooling results from 80 calories adsorbed 
during the melting process.

Antifreeze is a mixture of ethylene glycol and water.  It actually performs 
two functions in an automobile.  It depresses the freezing temperature of 
water and it elevates the boiling point of water so that your car's cooling 
system can operate over a wider temperature range.

So, I looked up the heat of fusion in my Handbook of Chemistry and Physics. 
 And the heat of fusion for ethylene glycol is 43.26 calories per gram, or 
about half of that of water.  So if you freeze a mixture of water and 
ethylene glycol, you will actually be storing less cooling energy than with 
pure water.  The mixture may be colder, but it will adsorb less energy.

There are a couple of other issues to consider, too.  Whenever you try to 
freeze a mixture, one component of the mixture will usually freeze first 
(often as a pure compound) leaving behind liquid with a different 
composition.  Therefore, if you attempt to freeze a water/antifreeze 
mixture, you will likely end up with an ice/antifreeze slush, rather than 
solid cubes of frozen water/antifreeze.  Every gram of liquid antifreeze in 
your slushy mixture represents lost cooling capacity compared with pure 
water.

Antifreeze is also poisonous.  Pets love it because it tastes sweet.  So if 
somebody gets hold of your green ice cubes or if you are sloppy with a dog 
or cat around, the results could be very bad.

The last issue to consider is the interaction between your skin and the 
water/antifreeze mixture.  It is possible to produce a water/antifreeze 
mixture that provides cooling at below the melting point of water (not as 
much cooling but colder).  You could alternately add salt to the melting 
ice to get the temperature of the mixture well below 0 C.  Problem is that 
these mixtures can also freeze the water in your skin.  We call that 
frostbite (you've seen pictures of frostbitten skin; black, dead, and very 
painful).  If you use a mixture of antifreeze/water or ice/salt on your 
body, the pain from the frostbite could be a lot worse than what your back 
is currently experiencing.  (When you freeze the water in your cells, it 
ruptures the cell membranes which hold your cells together - not a happy 
thing).  So, keep the antifreeze in the car; use salt to make homemade 
ice-cream and perhaps you might focus on white sand beaches with fluffy 
clouds against a dark blue sky, in a far away place where your girlfriend 
thinks of you as a normal, attractive person....