how would the melting point of a substance be obtained if it sublimes before it melts?
2007-09-23 13:27:36 · 6 answers · asked by Anonymous in Science & Mathematics ➔ Chemistry
the melting point is the same as the freezing point.. so find the freezing point
2007-09-23 13:31:58 · answer #1 · answered by Kind Answer Giver 2 · 1⤊ 1⤋
Melting point and boiling point are dependant on the pressure on the system. This is why water boils at a lower temperature in Denver, CO than it does in New York, NY. The lower pressure in the mountains means the molecules have more freedom to space out and escape the intermolecular forces.
This is also why some recipies include a longer cooking time for that city; lowering boiling point means lower cooking temperature, means longer time need to completely cook the food.
Sublimation is the direct change from a solid to a gas without first passing through the liquid phase. This is the change that makes solid carbon dioxide (dry ice) into the gaseous form.
It is possible to liquify carbon dioxide. However, this requires an increase in the pressure on the system. The additional pressure will keep the molecules closer together as the temperature increases, so that they do not have the freedoms that the gaseous state allows.
According the phase diagram sourced below, The pressure on the system must be above 5.11 atm in order to liquify it and thus be able to measure its melting point. That is more than five times the normal pressure felt by the atmosphere.
2007-09-23 20:37:42 · answer #2 · answered by lhvinny 7 · 0⤊ 0⤋
Sublimation, like boiling, is affected by pressure. If you increase the sublimation temperature by elevating the pressure, it should be possible to obtain a melting point, which is virtually unaffected by pressure, because melting does not involve adding molecules to the atmosphere..
The main reason you will not reach the melting point as long as sublimation is taking place is that vaporization requires a considerable amount of heat, just as melting does. The heat used up in sublimation is not available to reach the melting point, let alone to cause the compound to melt.
2007-09-23 20:37:07 · answer #3 · answered by Anonymous · 0⤊ 0⤋
Sublimation is a very slow process, getting to a melting point should not be a problem.
2007-09-23 20:40:40 · answer #4 · answered by johnandeileen2000 7 · 0⤊ 1⤋
Measure its weight while it heats up?
2007-09-23 20:36:04 · answer #5 · answered by GCB-TO 3 · 0⤊ 1⤋
huh?
2007-09-23 20:33:05 · answer #6 · answered by dragon boy 2 · 0⤊ 1⤋