Is it possible to obtain a sample of ice from liquid water without ever putting the water in a freezer or other enclosure at a temperature below \(0^{\circ} \mathrm{C} ?\) If \(\mathrm{so}\) how might this be done?

Freezing point depression is a phenomenon that occurs when a substance's freezing point is lowered by the addition of another substance, such as a solute in a solvent. Consider salt sprinkled on icy roads: the salt dissolves in the ice (solid state water), creating a salt-water solution that has a lower freezing point than pure water. This means that the ice will melt at temperatures below the normal freezing point of water, which is 0°C.
This concept is not only useful for practical applications like de-icing but it is also critical in many industrial processes and in the study of antifreeze in biological organisms. In a laboratory, freezing point depression can be used to determine molecular weights of solutes in a solution. By measuring the degree to which the freezing point of a solvent is lowered by the addition of a solute, you can calculate the molar mass of the solute.
In our original exercise, the added component could be a solute, but it also hints at the possibilities of freezing water by methods that don't involve temperature alone, such as pressure alterations.

Phase diagrams are charts that show the state of matter at various pressures and temperatures. They tend to feature three regions representative of solids, liquids, and gases, along with lines that indicate the conditions under which equilibrium phase changes occur.
Take water, for example. On a phase diagram for water, you would see lines that indicate the temperatures and pressures at which water transitions between being a solid (ice), liquid (water), and gas (steam). It is notable that these diagrams also display a point known as the 'triple point,' where all three phases can coexist in equilibrium. Moreover, there's a 'critical point' where the distinction between liquid and gas phases ceases to exist.
Learning to read phase diagrams not only helps in visualizing the conditions for phase changes but also provides insight into phenomena such as freezing water under conditions that don't involve low temperatures, which ties directly into our exercise problem and solution.

Matter typically exists in one of three states: solid, liquid, and gas. These states are strongly dependent on temperature and pressure. At 1 atmosphere of pressure, we are familiar with water freezing at 0°C and boiling at 100°C, but these temperature points change at different pressures.

• Solid: Particles are closely packed in a regular pattern. Solids have a definite shape and volume.
• Liquid: Particles are close together with some ability to move around. Liquids have a definite volume, but not a definite shape.
• Gas: Particles are well separated with lots of room to move. Gases have neither definite volume nor shape.

When substances change from one state to another—like freezing or boiling—we call these transitions 'phase changes.' These are often shown as straight lines on a phase diagram, representing the equilibrium between phases under different conditions of temperature and pressure. The 'step-by-step solution' to our exercise utilizes these principles to imagine freezing water without a low temperature by altering pressure.