![]() However, dissolved solutes in water increase the entropy of the water molecules, and so the compromise between lowering energy and maximising entropy occurs at a lower temperature. Solutes scarcely dissolve in ice, so the entropy of ice is unaffected by their presence. Entropy is more important at high temperatures, so fluids form at high temperatures and solids at low. Molecules in ice have lower energy than they do in liquid water, because they are more strongly attracted to their neighbours, but they also have lower entropy because they cannot move about. How does osmotic depression of freezing work? Like many effects at equilibrium, freezing involves a compromise between minimising energy and maximising entropy. For each mole of dissolved molecules or ions one adds to a kilogram of water, one lowers the equilibrium freezing point by (approximately) two degrees. The osmotic depression of freezing point has been known for a long time. The freezing point of water may be lowered by the osmotic effects of dissolved solutes or by the hydration effects of macromolecules or biological ultrastructures such as membranes. Which solutes are best at preserving ultrstructure? and.Which solutes are best at preventing freezing?, and.We also give very brief answers to two FAQs that have been raised by this page: Below we give references to this and other more formal and quantitative explanations in scientific journals. Some of the material in this short, informal essay is from the scientific paper " What is 'unfreezable water', how unfreezable is it and how much is there?" (Wolfe et al, 2002). Here we give a brief explanation of the phenomenon in terms of the effects that slow or prevent freezing under various experimental conditions. Water that doesn't freeze under certain conditions is sometimes called 'unfreezable water' by various workers in the fields of cryobiology, anhydrobiology, food science and elsewhere. ![]()
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