Why doesn't a pure liquid in a distilling flask vaporise all at once when the boiling temperature is reached?

Answer 1

That's because it requires a lot of energy to convert the liquid to the vapor phase - even for just converting (for example) water at 100 °C to water vapor that is also at 100 °C.

So, for example, once the water is at the boiling point (around 100 °C, depending on the exact air pressure), you need to add A LOT of heat to convert all the water to water vapor; in fact, much more than you needed to heat the water up to 100 °C.

Answer 2

when the boiling point is reached, the molecules in the liquid will collide with each other very erratically. so molecules gain mass times velocity(momentum) and escape out of the liquid surface.

but it has to have a trajectory path towards the liquid surface to get it vapourized. at boiling point, due to collisions they follow different path and may approach the walls of the distillation column or the container. so not the whole of liquid escapes at once.

consider this eg.

splash water on a flat surface. they evaporate quickly than the one in a puddle or any hollow container.

Answer 3

No, because the bonds are not broken at the same time within the molectule.

Answer 4

Boiling does not happen all at one. Once the boiling point is reached, temperature will not change until the vaporization has completed.

Answer 5

Even when water is at is boiling point, additional energy is needed for the water to transition from a liquid to a gas.

Answer 6

The molecules at the surface are under less pressure and as a result vaporize first.

Answer 7

During the change in state from liquid to gas, the bonds among molecules are not broken all at once, so the whole thing doesn't evaporate all at once either.