Frequently asked intresting facts - 2

What is triple point or what is its significance or what is the difference between triple point and critical point?

 There are 15 possible diagrams in Thermodynamics which are made with the different-different combination of 6 Thermodynamic properties which are pressure, temperature, volume, internal energy, enthalpy and entropy. Now all these 15 diagrams are constructed by taking a reference point on which all the three form of water exist, that's solid, liquid and gas. That point is known as triple point. Actually if we observe in detail, triple point is not a point in 14 out of 15 diagrams. It is a line and this line is known as triple line. Let me show you in example of 1 diagram out of those 14, that's temperature vs entropy diagram as shown below
Likewise 14 diagrams are there on which triple point is a line.
Only one diagram is there in which triple point is a point and that is pressure vs temperature diagram. In this diagram phase change region is also absent. Pressure vs temperature diagram for a general substance is shown below-

On all other 14 diagrams triple point is not a point and phase change region is also present.

Remember don't confused between triple point and critical point they both are different. critical point is a point on a phase diagram at which both the liquid and gas phases of a substance have the same density and are therefore indistinguishable.

There is also one important significance of triple point of water and that is -
The Kelvin temperature scale is absolute thermodynamic temperature scale which has single point of reference and that reference point is triple point of water. With the help of it we can define 1 kelvin. 1 kelvin is 1/273.16 triple point of water.

Why does temperature increases in compressor ?
As we all know that compressor deals with air. As the air moves into compressor it gets compress or we can say that it's pressure will increase due to which random motion per unit molecules increases, which increases the energy associated per unit molecules of gas and temperature itself is defined as energy associated per unit molecule thus with increase in pressure of gasses always leads to increase in temperature of gasses. Now that was physical explanation, mathematically also we can explain it. Air is perfect gas which follows ideal gas equation that's PV = mRT
From here pressure is directly proportional to temperature therefore with increase in pressure results in increase in temperature.

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