h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

While the term "freezing point" may be normal in everyday conversation, the actual definition is the triple point (the temperature at which all three phases of water can exist simultaneously).

Actually, the way I learnt it, 0°C/32°F is MELTING point of ice, because water actually needs to be at a lower temperature to freeze, because of the (negative?) energy required for solidification.

Or have I mixed something up??

Nope, I think the first point is technically correct...

To explain it in a _very_ unscientific way (I'll probably get lynched by the next passing after this one )

Remove heat energy from water and for every unit of energy you'll get a corresponding drop in temperature, until you reach 0°C when the reduction in the energy in the water actually causes it to solidify rather than to reduce in temperature, once it's frozen - removing more heat energy once again results in a temperature decrease...


The graph looks something like this...




Temperature
|
|||||------ (O°C)
||__________________Energy decrease

(And if that graph actually works considering the limitations of posting formating on this site I deserve a )

Nope, I think the first point is technically correct...

To explain it in a _very_ unscientific way (I'll probably get lynched by the next passing after this one )

Remove heat energy from water and for every unit of energy you'll get a corresponding drop in temperature, until you reach 0°C when the reduction in the energy in the water actually causes it to solidify rather than to reduce in temperature, once it's frozen - removing more heat energy once again results in a temperature decrease...


The graph looks something like this...




Temperature
|
|||||------ (O°C)
||__________________Energy decrease

(And if that graph actually works considering the limitations of posting formating on this site I deserve a )

Weird, it worked in preview mode

Try again




Temperature
|
|||||------ (O°C)
||__________________Energy decrease

Forget it... I'm getting a completely different output in preview mode as appears on the screen...

high school chemistry: energy is required for something to change phase, that is, go form solid to liquid or liquid to gas. So if you are trying ot make ice, .... actually it's easier to explain raising the temperature. So say you want to melt some ice. Put in heat energy until it's 0° C. At this point, it's still solid. You continue putting energy into it, but the temperature stays the same. Huh? you say? All the energy is going into breaking the hydrogen bonds between the water molecules. After a bit, it will all be melted, and then the temperature will start to go up again. If you want, i can explain the interesting parts of boiling, too. And i'm going to attempt a little graph.

temperature is the vertical axis, going up.

_/
_/
/
energy put in ->

does that work? the horizontal spots are the phase changes, parts going up are solid warming then liquid warming then gas warming.

wow, i really am a well, i had a reeeeally good chem teacher....and it was only last year....

Roughly what I was trying to say...

(and h2g2 doesn't seem to like my backslash button \\\