freezing point

Examples of freezing point in the following topics:

• Freezing Point Depression

  • 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 value of 0.93 oC is the change in the freezing point.
  • Discuss the effects of a solute on the freezing point of a solvent

• Farenheit Scale

  • In the Fahrenheit scale, the freezing of water is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees.
  • On this scale, water's freezing point is defined to be 32 degrees, while water's boiling point is defined to be 212 degrees.
  • The Fahrenheit system puts the boiling and freezing points of water exactly 180 degrees apart.
  • Therefore, a degree on the Fahrenheit scale is 1/180 of the interval between the freezing point and the boiling point.
  • On the Celsius scale, the freezing and boiling points of water are 100 degrees apart.

• 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.

• Phase Changes and Energy Conservation

  • The opposite happens when water freezes.
  • If that amount of energy is added to a mole of that substance at boiling or freezing point, all of it will melt or boil, but the temperature won't change.
  • At this point, there is a mixture of both ice and water.
  • The curve ends at a point called the critical point, because at higher temperatures the liquid phase does not exist at any pressure.
  • In this typical phase diagram of water, the green lines mark the freezing point, and the blue line marks the boiling point, showing how they vary with pressure.

• Celsius Scale

  • From 1743 until 1954, 0°C was defined as the freezing point of water, and 100°C was defined as the boiling point of water, both at a pressure of one standard atmosphere, with mercury as the working material.
  • Although these defining correlations are commonly taught in schools today, by international agreement the unit "degree Celsius" and the Celsius scale are currently defined by two different temperatures: absolute zero and the triple point of Vienna Standard Mean Ocean Water (VSMOW; specially purified water).
  • The temperature of the triple point of water is defined as precisely 273.16K and 0.01°C.
  • In this typical phase diagram of water, the green lines mark the freezing point, and the blue line marks the boiling point, showing how they vary with pressure.

• Crystalline Solids

  • However, if the solid melts, or the liquid freezes, a discontinuity occurs and the temperature of the sample remains constant until the phase change is complete.
  • 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.
  • 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.

• 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).

• 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.

• Change from another angle

  • ., ‘Kurt Lewin's change theory in the field and in the classroom: Notes toward a model of managed learning') Since good habits are recognized as being just as difficult to break as bad habits, the analogy the two men make is to unfreeze bad habits and freeze improved habits once they've been established.
  • Examples of how some businesses get their employees to admit that waste reduction is needed is to involve them in estimating the amount (and cost) of the waste the business produces, analyzing energy and fuel consumption, offering carbon emission estimates, and/or pointing out garbage levels and costs.
  • Freeze new behaviours.

• Latent Heat

  • Conversely, water freezes in an ice tray cooled by lower-temperature surroundings .
  • Conversely, energy is released during freezing and condensation, usually in the form of thermal energy.
  • Note that melting and vaporization are endothermic processes in that they absorb or require energy, while freezing and condensation are exothermic process as they release energy.
  • Even more energy is required to vaporize water; it would take 2256 kJ to change 1 kg of liquid water at the normal boiling point (100ºC at atmospheric pressure) to steam (water vapor).
  • That same energy must be removed for freezing to take place.