Can you tell me all you know about Melting point and boiling point?

Answer 1

The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point.

For most substances, melting and freezing points are equal. For example, the melting point and freezing point of the element mercury is 234.32 kelvin (−38.83 °C or −37.89 °F). However, certain substances possess differing solid-liquid transition temperatures. For example, agar melts at 85 °C (185 °F) and solidifies from 32 °C to 40 °C (89.6 °F to 104 °F); this process is known as hysteresis. Certain materials, such as glass, may harden without crystallizing; these are called amorphous solids.

The melting point of water at 1 atmosphere of pressure is 0 °C (32 °F, 273.15 K), this is also known as the ice point. In the presence of nucleating substances the freezing point of water is the same as the melting point, but in the absence of nucleators water can supercool to −42 °C (−43.6 °F, 231 K) before freezing.

Unlike the boiling point, the melting point is relatively insensitive to pressure. Melting points are often used to characterise organic compounds and to ascertain the purity. The melting point of a pure substance is always higher than the melting point of that substance when a small amount of an impurity is present. The more impurity is present, the lower the melting point. Eventually, a minimum melting point will be reached. The mixing ratio that results in the lowest possible melting point is known as the eutectic point.

The chemical element with the highest melting point is tungsten, at 3695 K (3422 °C, 6192 °F). The often-cited carbon does not melt at ambient pressure but sublimates at about 4000 K; a liquid phase only exists above pressures of 10 MPa and estimated 4300–4700 K. Tantalum hafnium carbide (Ta4HfC5) is a refractory compound with a very high melting point of 4488 K (4215 °C, 7619 °F).[1] At the other end of the scale, helium does not freeze at all at normal pressure, even at temperatures infinitesimally close to absolute zero; pressures over 20 times normal atmospheric pressure are necessary


The boiling point of a substance is the temperature at which it can change its state from a liquid to a gas throughout the bulk of the liquid at a given pressure. A liquid may change to a gas at temperatures below the boiling point through the process of evaporation. Any change of state from a liquid to a gas at boiling point is considered vaporization. However, evaporation is a surface phenomenon, in which only molecules located near the gas/liquid surface could evaporate. Boiling on the other hand is a bulk process, so at the boiling point molecules anywhere in the liquid may be vaporized, resulting in the formation of vapor bubbles.

A somewhat clearer (and perhaps more useful) definition of boiling point is "the temperature at which the vapor pressure of the liquid equals the pressure of the surroundings."


Something that should be remembered is that boiling is evidenced by the appearance of bubbles containing vapor from the liquid. [Note: The bubbles that precede real boiling in the pot on the stove are either (formerly) dissolved gas or water vapor forming on the very hot bottom of the pot that will be condensed before it can get to the top of the liquid.] Production of vapor requires energy and thus does not occur without some source of energy. This source can be a hot surface or even the liquid itself. Hot liquid will boil as it rises through the bulk liquid if the pressure of the environment drops to the vapor pressure of the liquid at its temperature. This production of vapor will not quickly stop because the temperature of the liquid will not be reduced by the vaporization thus reducing the vapor pressure.


[edit] Saturation temperature and pressure
A saturated liquid or saturated vapor contains as much thermal energy as it can without boiling or condensing.

Saturation temperature means boiling point. The saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapor phase. The liquid can be said to be saturated with thermal energy. Any addition of thermal energy results in a phase change.

If the pressure in a system remains constant (isobaric), a vapor at saturation temperature will begin to condense into its liquid phase as thermal energy (heat) is removed. Similarly, a liquid at saturation temperature and pressure will boil into its vapor phase as additional thermal energy is applied.

The boiling point corresponds to the temperature at which the vapor pressure of the substance equals the ambient pressure. Thus the boiling point is dependent on the pressure. Usually, boiling points are published with respect to standard pressure (101.325 kilopascals or 1 atm). At higher elevations, where the atmospheric pressure is much lower, the boiling point is also lower. The boiling point increases with increased ambient pressure up to the critical point, where the gas and liquid properties become identical. The boiling point cannot be increased beyond the critical point. Likewise, the boiling point decreases with decreasing ambient pressure until the triple point is reached. The boiling point cannot be reduced below the triple point.

Saturation Pressure, or vapor point, is the pressure for a corresponding saturation temperature at which a liquid boils into its vapor phase. Saturation pressure and saturation temperature have a direct relationship: as saturation pressure is increased so is saturation temperature.

If the temperature in a system remains constant (an isothermal system), vapor at saturation pressure and temperature will begin to condense into its liquid phase as the system pressure is increased. Similarly, a liquid at saturation pressure and temperature will tend to flash into its vapor phase as system pressure is decreased.


[edit] Latent heat
The process of changing from a liquid to a gas requires an amount of heat called the latent heat of vaporization. As heat is added to a liquid at its boiling point, all of this heat goes toward the phase change from liquid to gas, thus the temperature of the substance remains constant even though heat has been added. The word latent, which comes from Latin and means hidden, is used to describe this "disappearing" heat that is added, but doesn't result in an increase in temperature. Since heat is added with no corresponding change in temperature, the heat capacity of the liquid is essentially infinite at the boiling point.


[edit] Intermolecular interactions
In terms of intermolecular interactions, the boiling point represents the point at which the liquid molecules possess enough heat energy to overcome the various intermolecular attractions binding the molecules into the liquid (eg. dipole-dipole attraction, instantaneous-dipole induced-dipole attractions, and hydrogen bonds). Therefore the boiling point is also an indicator of the strength of these attractive forces.

The boiling point of water is 100 °C (212 °F) at standard pressure. On top of Mount Everest the pressure is about 260 mbar (26 kPa) so the boiling point of water is 69 °C.

For purists with a knowledge of thermodynamics, the normal boiling point of water is 99.97 degrees Celsius (at a pressure of 1 atm, i.e. 101.325 kPa). Until 1982 this was also the standard boiling point of water, but the IUPAC now recommends a standard pressure of 1 bar (100 kPa). At this slightly reduced pressure, the standard boiling point of water is 99.61 degrees Celsius.


[edit] Properties of other elements
The element with the lowest boiling point is helium. Both the boiling points of rhenium and tungsten exceed 5000 K at standard pressure. Due to the experimental difficulty of precisely measuring extreme temperatures without bias, there is some discrepancy in the literature as to whether tungsten or rhenium has the higher boiling point.

(Cf. DeVoe, Howard, Thermodynamics and Chemistry. Prentice-Hall, 2001)

Answer 2

Melting point is the point where particles in a substance have enough thermal energy (combination of kinetic and potential) so they can now slip past each other instead of staying in the crystal structure of the solid. The heat that the material must gain for the material to do this is called it's heat of fusion.
Boiling point is the temperature at which a substance begins to vaporize but pressure is also a consideration. For example, water will begin boiling at 100 degrees Celsius if it is at sea level. But since it is pressure dependent then it will boil at a lower temperature if the pressure outside the substance is lower (like up on a mountain). A substance will boil if enough energy is added to it, and this energy increases the pressure within the substance. When the pressure within a substance is greater than the pressure outside a substance, the substance will boil and it's boiling point has been reached. Boiling point is dependent on Pressure AND Temperature.
The heat needed to boil (or vaporize) an amount of stubstance is called it's heat of vaporazation.

Answer 3

The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point.

For most substances, melting and freezing points are equal. For example, the melting point and freezing point of the element mercury is 234.32 kelvin (−38.83 °C or −37.89 °F). However, certain substances possess differing solid-liquid transition temperatures. For example, agar melts at 85 °C (185 °F) and solidifies from 32 °C to 40 °C (89.6 °F to 104 °F); this process is known as hysteresis. Certain materials, such as glass, may harden without crystallizing; these are called amorphous solids.

The melting point of water at 1 atmosphere of pressure is 0 °C (32 °F, 273.15 K), this is also known as the ice point. In the presence of nucleating substances the freezing point of water is the same as the melting point, but in the absence of nucleators water can supercool to −42 °C (−43.6 °F, 231 K) before freezing.

Unlike the boiling point, the melting point is relatively insensitive to pressure. Melting points are often used to characterise organic compounds and to ascertain the purity. The melting point of a pure substance is always higher than the melting point of that substance when a small amount of an impurity is present. The more impurity is present, the lower the melting point. Eventually, a minimum melting point will be reached. The mixing ratio that results in the lowest possible melting point is known as the eutectic point.

The chemical element with the highest melting point is tungsten, at 3695 K (3422 °C, 6192 °F). The often-cited carbon does not melt at ambient pressure but sublimates at about 4000 K; a liquid phase only exists above pressures of 10 MPa and estimated 4300–4700 K. Tantalum hafnium carbide (Ta4HfC5) is a refractory compound with a very high melting point of 4488 K (4215 °C, 7619 °F).[1] At the other end of the scale, helium does not freeze at all at normal pressure, even at temperatures infinitesimally close to absolute zero; pressures over 20 times normal atmospheric pressure are necessary.

Answer 4

Melting point is the temperature at which a solid turns to liquid at a given pressure.
Boiling point is the temperature at which the atmospheric pressure is equal to the pressure of the of the vapor just above the liquid.

Answer 5

Melting point is the temperature at which a solid becomes liquid.
Boiling point is the temperature at which a substance boils.

Answer 6

they are the temperatures at which a substance changes between solid and liquid, and liquid and gas, respectively. for water, melting/freezing point is 0 deg C, and boiling point (which turns it into steam) is 100 deg C, but all substances have different melting and boiling points.

Answer 7

Of what?

Different elements or combination of elements melt or boil at different temperatures. Granite will boil at a high enough temperature and Oxygen will liquefy at a low enough temperature.

Scientific experimentation uses several temperature scales. Fahrenheit, Celsius, Kelvin, and Centigrade are the most widely known.

Answer 8

melting point is when a solid turns into a liquid and boiling point is when a liquid turns into gas/vapor. the temp varies depending on the substance.

Answer 9

well in celcius the melting 0 and the boiling is 100 feherenhiet however is much hsrder to remember..... 32- freezing
boiling.....?

Answer 10

boilin point is where a solid goes to a liquid
100 degree celcius, 212 dgrees farenheit, and 343 kalvin melting point is where a slid goes to a liquid