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## partial molar quanitity

I am quite confusing about the concept of partial molar quanitity and partial pressure. why there is no a partial molar pressure and what is the difference between partial molar pressure(if it exists) and partial pressure and why no partial molar temperature or partial temperature.

jmlo 2013-11-13 12:49 AM

## 回覆 1# 的帖子

Note that partial molar quantities are defined only for extensive properties which are dependent upon the size of the system. Since both pressure and temperature are intensive properties (i.e., they are independent of the system size), no corresponding partial molar quantities can be defined properly.

## 回覆 2# 的帖子

Then why there exist partial pressure?

jmlo 2013-11-15 01:04 PM

## 回覆 3# 的帖子

Note that partial molar quantities are defined with the constraints of constant temperature and pressure. For any extensive property of a system, it can be written as a function of T, P and n where n is the number of moles of the components. One can obtain the partial molar quantity of this extensive property by taking the partial derivative with respect to n while keeping T and P constant.

On the other hand, partial pressure is not a partial molar quantity since it is not given at constant pressure. It tells you how one component of a gas mixture contributes to the overall pressure only.