Why is ice a good coolant
As Cold mixture are mixtures of substances that are used to generate cold.
The effect of the cold mixture uses three effects.
- The process of dissolving substance A in substance B can be endothermic. Example 2 in the table uses this effect.
- The cooling substance is subject to a phase transition, the temperature that can be reached is then the phase transition temperature. This case is implemented in example 1.
- By adding an additive, the melting point of a substance can be lowered significantly. An example of this is shown in row 4 of the table. The physical causes of this effect are explained in the article Melting point depression.
In contrast to refrigerants, most refrigeration mixtures can be stored separately without a pressure vessel. For this reason, refrigeration mixtures are often used when low temperatures are to be generated with simple means and kept briefly without a refrigeration machine (e.g. in the laboratory).
When processes for the mechanical production of refrigeration and refrigerants were still unknown, i.e. before 1900, refrigeration mixtures were used to produce refrigeration artificially.
Cold mixtures with salts
Cold mixtures of salts with water or water ice use the endothermic heat effects when dissolving substances for cooling.
The change in temperature during dissolution results from the energy that is necessary to dissolve the ionic lattice of the salts and the hydration energy that is released during dissolution. In the case of salts with a lattice energy greater than the hydration energy, the mixture removes the missing energy from the environment and the solution cools down.
Cold mixtures of salts in water can reach temperatures as low as -15 ° C (*). Better results are achieved with mixtures with water ice, down to -55 ° C (The lowest temperatures can only be achieved when using a dewar flask.). Mixing with ice adds cooling due to the melting of the ice and the subsequent endothermic dissolution of the salt in the melt water.
Cold mixes with dry ice
Cold mixtures with dry ice can reach temperatures as low as -90 ° C (*). Dry ice is used in methanol (down to -70 ° C (*)), in acetone (down to -80 ° C) and in diethyl ether (down to -90 ° C (*)).
Even lower temperatures can only be achieved with liquefied gases.
Common cold mixtures
|composition||Min. Temperature (° C)||Amount of heat (kJ)|
|100 g water + 100 g ice||0||-|
|100 g water + 74 g NaNO3||-5||-|
|100 g water + 244.8 g CaCl2 · 6 H.2O||-12||-|
|100 g ice + 33 g NaCl||-21.3||-|
|100 g ice + 81.8 g CaCl2 · 6 H.2O||-22||-|
|100 g ice + 28.2 g MgCl2||-33||-|
|100 g ice cream + 92.3 g H2SO4 66%||-37||-|
|100 g ice + 122.2 g CaCl2 · 6 H.2O||-40||-|
|100 g ice + 143.9 g CaCl2 · 6 H.2O||-55||-|
|Alcohol + CO2 (firmly)||-78||-|
|Acetone + CO2 (firmly)||-78||-|
|Ether + CO2 (firmly)||-82||-|
Category: Mixture of substances
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