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Does the salt water requires more energy to be freezed with a fridge compared to distilled water?

If so, why and how much more?

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  • $\begingroup$ I suspect it depends from the nature of the salt,if during the dissolution in water we are in presence of an esothermic reaction,during the freezing we need less enegy to make ice,and viceversa,if i dissolve a salt that react in an endothermic process,we need more energy to freeze... Is that true? $\endgroup$ – Gabriele Citossi Jun 11 '17 at 19:25
  • $\begingroup$ Would Chemistry be a better home for this question? $\endgroup$ – Qmechanic Jun 11 '17 at 20:01
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    $\begingroup$ If the water freezes slowly (the normal mode of freezing), the ice is composed of fresh water. Within this context, I'm not sure that your question makes sense. $\endgroup$ – David White Jun 11 '17 at 20:16
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thats a two pronged problem. It takes less energy to cool saltwater from 10 degrees C to 0 degrees C (because Heat Capacity is less) but saltwater freezes at lower temperature (-1.91 degrees C). So while its a little easier to cool, you have to cool it almost 2 degrees further to freeze it. The amount of heat to freeze is known at latent heat of fusion. I can't find a difference for the latent heat value so I'll assume they are equal. Hence after reaching freezing point, it takes same loss of energy to freeze (change phase) of salt water and fresh water. Without knowing the mass of the water I'd guess it takes a little less effort to cool and freeze saltwater. If you need a more complete answer give the mass of the water. I assumed they the same mass for fresh water and saltwater. Answer also depends on the salinity (how salty) of the salt water. The differences are maximized at a certain level of 'saltiness'.

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  • $\begingroup$ Thanks for your answer. I'd like to know if 1kg of fresh water with 35g of salts (Ocean water) dissolved are easier to freeze compared to 1Kg of fresh water. If your statement is true it should so be easier... $\endgroup$ – Gabriele Citossi Jun 11 '17 at 20:12
  • $\begingroup$ I computated about 3000J more for the phase change. Which is the Cp of sea water from 300K to 271.01? $\endgroup$ – Gabriele Citossi Jun 11 '17 at 20:21
  • $\begingroup$ ok,about 95% of fresh water $\endgroup$ – Gabriele Citossi Jun 11 '17 at 20:51
  • $\begingroup$ From some tables,salty water has less latent heat $\endgroup$ – Gabriele Citossi Jun 14 '17 at 17:07

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