I understand that at boiling point, vapour pressure becomes equal to the external pressure. But in my textbook it is written that at boiling point liquid and vapour exist in equilibrium. What does it mean by 'vapour and liquid exist in equilibrium' and also why do they exist in equilibrium?
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Please edit your answer to identify the textbook and give the complete quote and context. A liquid and its vapor can be at equilibrium over a wide variety of conditions, not just boiling point at atmospheric pressure. "Equilibrium" broadly means that there are no intensive-property gradients that would tend to drive the system to evolve. – Chemomechanics Apr 18 '21 at 17:02
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In a closed container at a fixed temperature, the rate at which molecules leave the liquid is equal to the rate at which they return. Boiling in a liquid occurs when the temperature at the bottom allows bubbles to form and grow. The vapor pressure in the bubble must equal that of the surrounding liquid. The bubbles are almost like closed containers.
R.W. Bird
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Does this mean that at boiling point the rate of change of liquid into gas is equal to the rate of change of gas into liquid? – RIPAN BARUAH Apr 19 '21 at 07:26
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If you are seeing bubbles coming to the surface in an open container, you are losing liquid. – R.W. Bird Apr 19 '21 at 13:19