Question

what do you mean by triple point??why is it used as a standard in thermometry?

Answer 1

triple point defines a definite temperature and pressure where all the three states of the substabce occur simultaneously..
for ex triple point of water is at 273.16 K and 4.58 hg of mercury

Answer 2

but how can three states exist together?

Answer 3

the three states exist together in equilibrium......

The single combination of pressure and temperature at which liquid water, solid ice, and water vapour can coexist in a stable equilibrium occurs at exactly 273.16 K (0.01 °C) and a partial vapour pressure of 611.73 pascals (ca. 6.1173 millibars, 0.0060373 atm). At that point, it is possible to change all of the substance to ice, water, or vapor by making arbitrarily small changes in pressure and temperature. Even if the total pressure of a system is well above triple point of water, provided the partial pressure of the water vapour is 611.73 pascals then the system can still be brought to the triple point of water. Strictly speaking, the surfaces separating the different phases should also be perfectly flat, to abnegate the effects of surface tensions.

The gas–liquid–solid triple point of water corresponds to the minimum pressure at which liquid water can exist. At pressures below the triple point (as in outer space), solid ice when heated at constant pressure is converted directly into water vapour in a process known as sublimation. Above the triple point, solid ice when heated at constant pressure first melts to form liquid water, and then evaporates or boils to form vapor at a higher temperature.

For most substances the gas–liquid–solid triple point is also the minimum temperature at which the liquid can exist. For water, however, this is not true because the melting point of ordinary ice decreases as a function of pressure, as shown by the dotted green line in the phase diagram. At temperatures just below the triple point, compression at constant temperature transforms water vapor first to solid and then to liquid.

Answer 4

for water!!

Answer 5

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Answer 6

what happened??

Answer 7

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Answer 8

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Answer 9

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Answer 10

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Answer 11

thanks

Answer 12

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Answer 13

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Answer 14

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Answer 15

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Answer 16

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