freezing point depression

Examples of freezing point depression in the following topics:

• Freezing Point Depression

  • Freezing point depression is a colligative property observed in solutions, brought on by the introduction of solute molecules to a solvent.
  • Freezing point depression is the phenomena that describes why adding a solute to a solvent results in the lowering of the freezing point of the solvent.
  • The freezing point depression can also be explained in terms of vapor pressure.
  • In this equation, $\Delta T_f$ is the freezing point depression, Kf is the freezing point depression constant, and i is the van 't Hoff factor.
  • The freezing point depression constant changes depending on the solvent, and the van 't Hoff factor accounts for the number of particles that a dissolving solute creates in solution.

• Liquid to Solid Phase Transition

  • Freezing is a phase transition in which a liquid turns into a solid when its temperature is lowered to its freezing point.
  • Freezing, or solidification, is a phase transition in which a liquid turns into a solid when its temperature is lowered to or below its freezing point.
  • For most substances, the melting and freezing points are the same temperature; however, certain substances possess different solid-liquid transition temperatures.
  • The melting point of water at one atmosphere of pressure is very close to 0 °C (32 °F, 273.15 K), and in the presence of nucleating substances the freezing point of water is close to the melting point.
  • But heat must be continually removed from the freezing liquid, or the freezing process will stop.

• Crystalline Solids

  • For a given compound, this temperature represents its melting point (or freezing point), and is a reproducible constant as long as the external pressure does not change.
  • Now it is well known that the freezing point of a solvent is lowered by a dissolved solute, e.g. brine compared with water.
  • If two crystalline compounds (A & B) are thoroughly mixed, the melting point of that mixture is normally depressed and broadened, relative to the characteristic sharp melting point of each pure component.
  • The lowest mixture melting point, e, is called the eutectic point.
  • Melting or freezing takes place over a broad temperature range and there is no true eutectic point.

• Solid to Gas Phase Transition

  • But at temperatures below that of the triple point, a decrease in pressure will result in a phase transition directly from the solid to the gaseous.
  • This is because the pressure of their triple point is very high and it is difficult to obtain them as liquids.
  • Even ice has a measurable vapor pressure near its freezing point, as evidenced by the tendency of snow to evaporate in cold dry weather.
  • Notice the triple point of the substance.
  • At temperatures and pressures below those of the triple point, a phase change between the solid and gas phases can take place.

• Major Features of a Phase Diagram

  • The major features of a phase diagram are phase boundaries and the triple point.
  • The triple point is the point on the phase diagram where the lines of equilibrium intersect -- the point at which all three distinct phases of matter (solid, liquid, gas) coexist.
  • At the triple point, water in the solid, liquid, and gaseous states coexist.
  • The green line marks the freezing point (or transition from liquid to solid), the blue line marks the boiling point (or transition from liquid to gas), and the red line shows the conditions under which a solid can be converted directly to a gas (and vice-versa).

• Physical and Chemical Properties of Matter

  • For example, the freezing point of a substance is a physical property: when water freezes, it's still water (H2O)—it's just in a different physical state.

• Temperature

  • They do not generate a number: they do not tell us that water freezes at 0 °C, or that it boils at 100 °C.
  • Isaac Newton proposed a thermometer with a scale of 12 degrees between the freezing and boiling points of water.
  • Anders Celsius proposed a 100 degree scale for the difference between freezing and boiling of water, and after a few minor adjustments, the Celsius, or centigrade, system was also widely adopted.
  • Celsius is a scale and unit of measurement for temperature where 0 °C is the freezing point of water.

• Three States of Matter

  • A solid can transform into a liquid through melting, and a liquid can transform into a solid through freezing.
  • When a solid is heated above its melting point, it becomes liquid because the pressure is higher than the triple point of the substance.
  • A liquid can be converted to a gas through heating at constant pressure to the substance's boiling point or through reduction of pressure at constant temperature.
  • The video also discusses melting, vaporization, condensation, and freezing.

• Volume and Density

  • At that point, the density trend reverses.
  • At 0 °C, water freezes to ice and floats.
  • The implications of this simple fact are enormous: when a lake freezes, ice crusts at the surface and insulates the liquid below from freezing, while at the same time allowing the colder water (with a temp of approx. 4 °C and a high density) to sink to the bottom.

• Mercury

  • With a freezing point of −38.83 °C and boiling point of 356.73 °C, mercury has one of the narrowest liquid state ranges of any metal.