Question

I don't understand this line
"At boiling point the saturated vapour pressure equals the atmospheric pressure and hence bubbles can be formed inside the liquid"

Vapour pressure as i know is the pressure exerted by the vapors on the walls of the container. I understand that at any temperature a liquid evaporates and thus there will be vapor and vapor pressure.. But i don't get how vapor pressure has something to do with formation of bubbles..

Answer 1

Also some textbook says that when water is heated to boiling point, the AIR that is dissolved in water .. ( i think O2 and other molecules) start bubbling


but some other says its the WATER VAPOR that are formed inside.. which means H20 molecules only are bubbling out..

plz help.. :P

Answer 2

vapor is liquid that turns into gas, if a liquid turns into gas at the bottom of the container it will move up to the surface in the form of a bubble..... so a lot of vapor pressure means u have a lot of gas particles being produced in the liquid so these gas particles all travel upto the surface and escape out of the liquid in the form of bubbles

Answer 3

ok..
see if you increase temperature of the liquid in a container, then you provide more energy to the molecules.. and thus the vapour pressure increases.. But vapour pressure only increases because there are more vapours being formed..

i don't get whats the big deal when the vapour pressure equals the atm. pressure? .. i mean how does that affect what happens INSIDE the volume of the liquid..

Answer 4

Stuck or something? :P

Answer 5

ok so...
Evaporation takes place inside the container when the liquid is heated, a build up of vapor pressure occurs inside the container. As more particles evaporate, vapor pressure increases. Inside a sealed container, the reverse process of condensation also occurs. Initially the rate of condensation is low due to small number of gas particles. As time goes by, the rate of condensation increases. At some point the rate of condensation will become equal to the rate of evaporation and the vapor phase is said to be equal to the liquid phase. The vapor pressure is at a maximum for the given temperature and this is known as the equilibrium vapor pressure. This is when boiling occurs and they say that its when the liquid's equilibrium vapor pressure must equal the external pressure exerted (which is the same as saying that the vapor pressure must equal the atmm pressure) on it because the gas particles cannot escape the liquid until they have same energy as the atm pressure inside the container.

so say the pressure above the surface of the water is really high, them the water particles must consume the same amount of energy that the air particle in the container have, before they can leave the liquid phase

i hope that helps, i cant explain better than that

Answer 6

I understand that..

but i don't understand how the vapor pressure has anything to do with what happens INSIDE THE LIQUID?..

how is that when the vapor pressure matches the atm pressure.. Bubbles are formed INSIDE THE LIquid..

is it like this??

bubbles are formed because liquid does get converted into gas inside the volume but just doesn't have enough energy to escape and so shrinks back down.. but when the vapour pressure hits the atm pressure, the bubbles have enough energy to escape??

i also don't understand how bubbles are formed inside?? i mean strictly speaking gas or liquid its basically the same liquid.. so if its water, then its a bubble of steam(h20) inside water (h20) itself?

Answer 7

yes, when vapor pressure equals atm pressure, the water molecules have the same energy as the atm pressure so now they can escape the liquid. And yes, its a bubble of steam h2O (i think), and the reason they form at the bottom of the container is because heat is applied at the bottom and the liquid at the bottom gains energy fastest so it turns into gas fastest

Answer 8

thanks a lot dude :)!!