# Are saturation temperature and boiling point same thing?

In my view they both are same thing. Boiling point is the temp at which vapor pressure of water becomes greater than pressure outside vessel. Liquid water change it's phase during this. And. At a given pressure the temperature at which a pure substance change it's phase is saturation temperature. At 101.325 kPa water boils at 100°C. So in my view it's saturation temperature should also be 100°C at 101.325 kPa.

But in Cengel Boles Thermodynamics book it is written that at pressure 101.325 kPa, saturation temperature of water is 99.97°C.

So is it a misprint or saturation temperature and boiling point are different?

• Probably a typo. According to the table Water/steam data table at standard pressure (0.1 MPa) in en.wikipedia.org/wiki/Water_(data_page) the boiling point is ~99.63C. They write stp as 100kPa and also "Note that the boiling point of 100.0 °C is at a pressure of 0.101325 MPa (1 atm), which is the average atmospheric pressure." The same is in www1.lsbu.ac.uk/water/water_properties.html Aug 25 '18 at 20:57

No they are not the same. The saturation temperature is the temperature at which the vapour pressure $p(T)$ of the liquid equals the partial pressure of the vapour in the ambient atmosphere. When $T$ is below saturation the vapour in the atmosphere will condense onto the liquid surface. When $T$ is above saturation the liquid will evaporate from the liquid surface until the local atmospheric vapour pressure has increased to that ($p(T)$) required for equilibrium with the liquid.
The boiling point is the temperature at which the vapour pressure of the liquid equals the total pressure of the surrounding atmosphere. The total pressure is (approximately) the sum of the vapour pressure in the atmosphere together with that of the other gaseos components ($O_2$ and $N_2$ etc.). When the liquid vapour pressure is greater that the total atmospheric pressure, the liquid can turn into vapour throughout the body of the liquid (i.e.boil) rather than merely evaporate from the surface.
• @user185991: I think the wiki article on Vapour Pressure is OK. On the "talk page" for your Boiling Point article that the error Boil=Sat and an number of other errors has been pointed out, but not corrected in the main text. It's always good to look at Wiki talk pages to see if there is a disagreement fight going on. One other place is to look up "dew point" as that is the same as the saturation temperature. As for the other disgreemnt, it is small and T$does have to be a bit over$T_sat\$ to boil becuse of surface tension effects. Aug 25 '18 at 21:30