Page 10 - che142 solutions ebook

THE IMPORTANCE OF RAOULT’S LAW

ASSUME A CLOSED CONTAINER IS FILLED

WITH A VOLATILE LIQUID A

AFTER SOME TIME, VAPOUR PARTICLES OF A

WILL START TO FORM

THE VAPOUR PARTICLES OF A WILL BE IN

DYNAMIC EQUILIBRIUM WITH THE LIQUID
PARTICLES (ON THE SURFACE)

THE PRESSURE EXERTED BY THE VAPOUR PARTICLES OF A AT ANY
PARTICULAR TEMPERATURE IS CALLED THE VAPOUR PRESSURE OF A AT
THAT TEMPERATURE

LIQUID B (SOLUTE) IS ADDED TO THE

CONTAINER

THIS WILL RESULT IN B PARTICLES

OCCUPYING THE SPACE BETWEEN A
PARTICLES ON THE SURFACE OF THE

SOLUTION

SINCE A LESSER NUMBER OF A PARTICLES IS ON THE SURFACE, THE

NUMBER OF VAPOUR PARTICLES OF A IN THE VAPOUR PHASE WILL BE
LESSER

THIS WILL RESULT IN LOWER VAPOUR PRESSURE OF A

IF B IS VOLATILE AS WELL, THERE WILL BE A LESSER NUMBER OF B

PARTICLES IN THE VAPOUR PHASE AS COMPARED TO PURE LIQUID B

THIS NEW PRESSURE (PARTIAL PRESSURE) OF EACH (A AND B)
IS GIVEN BY RAOULT’S LAW AND DEPENDS ON THE

CONCENTRATION OF EACH COMPONENT IN THE LIQUID PHASE

P X P X
A∝ A B ∝ B
= X P 0 = X P 0
A
B
B
A
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