The most exact 0 degree Celsius?

[alpha2cen]

0 degree Celsius is useful for the measuring standard.

How do we make it exactly?

[ydoaPs]

Freeze water.

[Mr Skeptic]

Put some pure ice and pure water, at sea level atmospheric pressure.

[alpha2cen]

Put some pure ice and pure water, at sea level atmospheric pressure.

 

Oxygen, nitrogen and carbon dioxide molecules are not contained in the water.

Practically it's not easy to storage in this condition.

Edited December 22, 2010 by alpha2cen

[between3and26characterslon]

0 degree Celsius is useful for the measuring standard.

How do we make it exactly?

 

 

Take a very small amount of ice at standard pressure, when it melts that's 0^oC

 

BTW if I remember correctly water freezes at about 4^oC, melts at 0^oC and doesn't exist between 0-4^oC this is due to the energy used or released during the phase transition between solid-liquid and liquid-solid. A mixture of ice and water will give an average temperature of 2^oC (for instance)

[alpha2cen]

 

BTW if I remember correctly water freezes at about 4^oC, melts at 0^oC and doesn't exist between 0-4^oC this is due to the energy used or released during the phase transition between solid-liquid and liquid-solid. A mixture of ice and water will give an average temperature of 2^oC (for instance)

 

In pure water the temperature liquid to solid phase transform is far from below the zero. If there were no nucleus for crystallization, the super cooled state would be maintained continuously.

[between3and26characterslon]

In pure water the temperature liquid to solid phase transform is far from below the zero. If there were no nucleus for crystallization, the super cooled state would be maintained continuously.

 

 

 

True, but...

 

wouldn't it freeze eventually ie. if you cooled it enough.

 

Then when you warm it back up again the temperature at which it melts will be 0^oC

[TonyMcC]

Because pure water in ice form can exist at temperatures below zero and in liquid form can exist above zero, for simple lab experiments zero is usually assumed when ice and water exist together as the ice melts. However I doubt this would be acceptable for calibrating instruments.

[CaptainPanic]

0 degree Celsius is useful for the measuring standard.

How do we make it exactly?

Experiments are never "exact".

 

That said, there are ways to make water very, very pure.

 

Supercooling should not be a problem. Just measure the temperature when ice is melting, not freezing.

 

The rest is about the definitions of Celsius. Wikipedia knows more than me (click!).

[alpha2cen]

True, but...

 

wouldn't it freeze eventually ie. if you cooled it enough.

 

Then when you warm it back up again the temperature at which it melts will be 0^oC

 

Rising temperature method to be 0^o C is not easy. It would be about 80 cal /g required to change from solid to liquid.

The problem is a heat transfer. In order to transfer heat to solid, temperature gradient is needed.

This method is not for making 0 degree.

Another method is like this.

First prepare pure solid ice and mix it with liquid water. At this time solid ice size should be small.

Problem is how to remove absorbed gas.

[CaptainPanic]

Rising temperature method to be 0^o C is not easy. It would be about 80 cal /g required to change from solid to liquid.

The problem is a heat transfer. In order to transfer heat to solid, temperature gradient is needed.

This method is not for making 0 degree.

Another method is like this.

First prepare pure solid ice and mix it with liquid water. At this time solid ice size should be small.

Problem is how to remove absorbed gas.

Vigorous mixing can make a temperature nearly uniform... of course, that is "uniform" for practical and industrial applications... not for measuring 0.0000000000 degrees C, at 10 decimals.

[alpha2cen]

Vigorous mixing can make a temperature nearly uniform... of course, that is "uniform" for practical and industrial applications... not for measuring 0.0000000000 degrees C, at 10 decimals.

Which digit can we make as the standard 0^oC?

100^oC data is quite exact. The data is 4-digit below zero.

[John Cuthber]

The SI unit of temperature is the Kelvin and it's not defined in terms of the normal freezing point of water (which varies with pressure) but the tipple point of water 273.16K (about 0.01C) where the pressure is also fixed.

 

Vigorous mixing would locally heat the mixture. The uniformity of temperature is ensured by making sure the system is well lagged.

Incidentally, water is perfectly capable of existing between 0 and 4 C.

This statement "BTW if I remember correctly water freezes at about 4oC, melts at 0oC and doesn't exist between 0-4oC this is due to the energy used or released during the phase transition between solid-liquid and liquid-solid. A mixture of ice and water will give an average temperature of 2oC (for instance) " is wrong in every major respect.

 

Any mixture of ice and water will be very close to 0C.

[between3and26characterslon]

The SI unit of temperature is the Kelvin and it's not defined in terms of the normal freezing point of water (which varies with pressure) but the tipple point of water 273.16K (about 0.01C) where the pressure is also fixed.

 

Vigorous mixing would locally heat the mixture. The uniformity of temperature is ensured by making sure the system is well lagged.

Incidentally, water is perfectly capable of existing between 0 and 4 C.

This statement "BTW if I remember correctly water freezes at about 4oC, melts at 0oC and doesn't exist between 0-4oC this is due to the energy used or released during the phase transition between solid-liquid and liquid-solid. A mixture of ice and water will give an average temperature of 2oC (for instance) " is wrong in every major respect.

 

Any mixture of ice and water will be very close to 0C.

 

So then I remembered incorrectly or I remembered correctly the wrong information. I thought the bonds that are created when water freezes required energy and these bonds were created at about 4^oC The amount of energy needed to make the bonds took the water down to 0^oC. That was my understanding. I also thought, going slightly off topic, that turning water at 100^oC into steam at 100^oC required energy for the same reason but perhaps I'm wrong there as well.

 

I would be grateful if you could set me sraight.

[mississippichem]

So then I remembered incorrectly or I remembered correctly the wrong information. I thought the bonds that are created when water freezes required energy and these bonds were created at about 4^oC The amount of energy needed to make the bonds took the water down to 0^oC. That was my understanding. I also thought, going slightly off topic, that turning water at 100^oC into steam at 100^oC required energy for the same reason but perhaps I'm wrong there as well.

 

I would be grateful if you could set me sraight.

 

 

The point where the three phases meet is the triple point John Cuthber refers to. At the triple point all three phases, solid, liquid, and gas are in equilibrium. Boiling points and freezing points are defined by the lines bordering the three regions on the graph and one can see how these are functions of pressure (y-axis) and temperature (x-axis). Notice how the triple point is defined by a point and not a line, meaning there is one specific temperature/pressure combination that will allow all three phases to be in equilibrium. That's why triple points are good foundations on which to build a temperature scale. Also, be careful not to confuse energy requirements of a phase transition with the temperature at which that transition occurs. Hope that helps.

[between3and26characterslon]

It does, thanks.

 

A bit anyway.

 

The triple point is at 0.603 atm, but what happens at 1 atm? For instance when we sweat is it not the phase transition from liquid to gas that cools us down? Will a molecule of water evaporate at less than 100^oC at 1 atm? Will water experience a sudden drop in temperature when it freezes at 1 atm?

 

I ask because I have more experience of 1 atm than 0.603 atm.

Edited December 23, 2010 by between3and26characterslon

[alpha2cen]

Macro phenomena is more simple than micro phenomena.

Kinetically what is the equilibrium.

.

(liquid water.....interface.......ice)surrounding system

.

At 0 C the molecules moves from ice to liquid water is similar to ice to liquid water.

When we insert some measuring instrument, thermal carrier( most of vibration energy)amount should not vary with very small amount of heat adding from the surroundings.

.

Other problem is water molecular state. Are near 0C liquid water molecules existed as monomer or as some weakly interacted polymeric mixture?

[alpha2cen]

I'm doubt about standard water.

Which water is the standard?

There are two kinds of oxygen, O¹⁶ and O¹⁸ in the Earth.

Between H₂O¹⁶ and H₂O (oxygen is O¹⁶ and O¹⁸ Earth average), which one can be used for standard?