Why does salt lower the temperature of Ice?

[ed84c]

Why does salt lower the temperature of Ice?

My physics teacher said it did and its complicated so i should find out. Any idea?

[5614]

i believe it is that the salt reacts with the water forming salt water! (seriously).

 

the freezing point of salt water is lower than the freezing point of water.

 

so say if it is -5C outside, water would have frozen, however salt water (which freezes at EG -10C) will not.... obviously this means that at very low sub-zero temperatures this effect is useless, however it is good and very useful and common chemical reaction which is used on roads throughout winter months and several countries.

[ed84c]

no its more complicated than that, even at room temp if you salt ice it will cool to a lower temperature (no thats NOT violating the 2nd law of TD)

[5614]

yeah, i dont get what the question is..... when salt is added to ice the ice melts because salt water freezes at a much lower point than water.

 

obviously the same effect would be observed in a warm room.

 

what i was saying was that say if you are in a room at near absolute zero (or anything really cold) then everything will freeze, salt of not!... i was saying an example.

[ed84c]

e.g. i put salt on an ice cube of temp -5*c.

 

It then becomes water at -10*c.

 

By the way if you dont know please leave it for somebdy else to answer

[5614]

ok, to convince you i did a quick googley search:

http://www.google.com/search?hl=en&q=Why+does+salt+lower+the+temperature+of+Ice%3F+

 

and found:

http://science.howstuffworks.com/question58.htm

(which is a trusted site)

[ed84c]

Here i found it from your search

 

When salt of room temperature is in contact with ice, the outer surface of the ice melts away. Subsequently, salt dissolves in the film of water on the surface of the melting ice to form brine. As the ice melts, it absorbs heat from this brine, making it colder (below zero degree Celsius). The water in the brine will not re-freeze due to the presence of salt particles. The interaction between the salt ions and the water molecules tends to separate the water molecules so that it is more difficult to arrange themselves into a fixed crystalline lattice. Thus, salt is said to lower the freezing point of water. Since the freezing point is lowered, the brine can give out more heat to the un-melted ice without being frozen. This lowers the temperature of the whole ice-salt mixture. It has been found that the addition of 29 parts common salt to 71 parts ice lower the temperature of the mixture to -21 degrees Celsius. [/Quote]

[5614]

ok, good good, so that clears that up

[swansont]

If you want more info, Google on "freezing point depression" (and/or "boiling point elevation" since it's a related phenomenon)

[mardener]

you are all poor at explaining something so simple.

[d22k]

where as YOU crafted a beutifully clear and concise explaination...