Question

Two liquids A and B boil at ${\text{14}}{{\text{5}}^{\text{0}}}{\text{C}}$ and ${\text{19}}{{\text{0}}^{\text{0}}}{\text{C}}$respectively. Which of them will have higher vapor pressure at ${\text{8}}{{\text{0}}^{\text{0}}}{\text{C}}$?

Answer 1

Vapor pressure is a quantity which tells us about the tendency of any substance to get changes into the gaseous form from its original state and this change will take place by providing heat through increasing the temperature.

Complete answer:
In the question two liquids are given and according to that, boiling point of liquid A is ${\text{14}}{{\text{5}}^{\text{0}}}{\text{C}}$ and of liquid B is ${\text{19}}{{\text{0}}^{\text{0}}}{\text{C}}$. Let have some light on the following points:
-Boiling point is that point where the vapor pressure of the surface liquid is equal to the pressure exerted by the surroundings on the liquid.
-As we know that vapor pressure of a liquid gives the knowledge about the tendency of that liquid to change into gaseous state, so for a liquid which has a high tendency of conversion will have low boiling point and easily get converted into gaseous form.
-From the above two points we conclude that vapor pressure and boiling point will have inverse relation i.e.
Vapor Pressure $\alpha$ $\dfrac{{\text{1}}}{{{\text{Boiling Point}}}}$
-In the question two liquids with two boiling points are given, so the liquid which have low boiling point will have higher vapor pressure and which have higher boiling point will have low vapor pressure.
So we conclude that liquid A whose boiling point is lower than B which is ${\text{14}}{{\text{5}}^{\text{0}}}{\text{C}}$ will have higher vapor pressure at ${\text{8}}{{\text{0}}^{\text{0}}}{\text{C}}$.

Note:
Here some of you may think that vapor pressure and boiling point may convey the same thought, but that assumption is wrong. They both are used to explain the same quantity but not convey the same meaning.