2007-07-22 13:24:19 · 6 answers · asked by Guy 1 in Science & Mathematics ➔ Chemistry
This usually happens during a phase change. If you look at a heating curve of a pure substance, the substance is being heated the whole time. But, you will see two "plateaus." In these portions of the graph, the temp remains constant. During the first plateau, the solid is changing into a liquid (melting). During the second, the liquid is changing into a gas (boiling).
The reason that the T does not increase during a phase change is that the heat added is being used to break intermolecular forces between the molecules, rather than make the molecules speed up and increase their kinetic energy (which we measure as an incease in temperature).
In other words, during a phase change heat energy is used to increase potential energy of the substance by breaking IMF's, and when its not changing phase, the heat energy is used to increase the kinetic energy of the substance.
2007-07-22 14:07:50 · answer #1 · answered by Noles H 2 · 0⤊ 0⤋
At the triple point. A certain temperature at which a particular gas is in solid ,liquid and gas state at the same time This can be achieved by lowering the pressure over the liquid state by means of a vacuum pump to a certain low pressure.
2007-07-22 21:36:46 · answer #2 · answered by max 3 · 0⤊ 0⤋
When any substance is changing state (phase) from Solid to liquid (and vice-versa), and from Liquid to Vapour (and Vice-versa).
Melting/Freezing and Vaporising/Condensing.
Each process absorbs or releases 'Latent Heat' ...(Hidden Heat ...not measurable with a thermometer or by touch).
(The heat amount is different for different substances).
e.g...Water freezing/melting = - or + 80cal/g (334J/g)
Water/steam vaporising/condensing + or - 540cal/g (2260J/g).
2007-07-22 20:50:23 · answer #3 · answered by Norrie 7 · 0⤊ 0⤋
When it is melting or boiling. Ice absorbs 90 cal/g to melt from ice to water at 0degC. Water absorbs 510cal/g to boil to steam at 100degC.
2007-07-22 20:29:22 · answer #4 · answered by steve_geo1 7 · 0⤊ 0⤋
When it's in the process of transferring the heat to something else down the chain at the same rate that it's absorbing heat!!!
Or, water at atmospheric pressure and 100C will absorb 540calories per gram and stay at 100C before flashing to steam!!!
Or, ice at atmospheric pressure and 0C will absorb 80calories per gram and stay at 0C before melting!!!
2007-07-22 20:29:01 · answer #5 · answered by Anonymous · 0⤊ 3⤋
thermophials photosynthisis
2007-07-23 00:02:07 · answer #6 · answered by Anonymous · 0⤊ 0⤋