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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?

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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.

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  • $\begingroup$ How could you explain the definition given in Wikipedia? Under the heading saturation temperature and pressure it starts with saturation temperature means boiling point. en.wikipedia.org/wiki/Boiling_point?wprov=sfla1 $\endgroup$
    – user185991
    Aug 25, 2018 at 21:13
  • $\begingroup$ @user185991: Which article are you looking at? I looked at "Saturation temperature" and got redirected to the article "vapor pressure" that says just what I wrote above... $\endgroup$
    – mike stone
    Aug 25, 2018 at 21:16
  • $\begingroup$ Just follow the link given in my last comment. There you can find a article heading Saturation temperature and Pressure if you want I can provide a screenshot of that :-P $\endgroup$
    – user185991
    Aug 25, 2018 at 21:19
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    $\begingroup$ @user185991: OK I found your article "Boiling point". The statement "Sat T =boil T" is wrong/misleading. It only holds when there are only two components" the liquid and its vapour in a closed system. $\endgroup$
    – mike stone
    Aug 25, 2018 at 21:20
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    $\begingroup$ @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. $\endgroup$
    – mike stone
    Aug 25, 2018 at 21:30

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