Why does liquid boil

It just evaporates at the speed needed to equal the amount of heat added to the water. If the heat is enough, it was boil. Once boiling starts, there is an equilibrium between the liquid and vapor phase. The pressure, temperature and partial molar Gibbs energy are equal for each phase so that water molecules have no preference for one phase or the other. That's for intensive variables. However, the total enthalpy of the liquid and vapor is not fixed : it keeps increasing as more energy is brought in.

The proportion of vapor to liquid is fixed through this energy balance. If the pressure is maintained externally, say by a piston, there is no possibility for the water bubbles to form at any other pressure than the vapor pressure. However when you boil water at the bottom of a pot, two phenomena alter the situation slightly. The first is the hydrostatic height of the water column, which increases the pressure at the bottom where bubbles form and raises the equilibrium temperature.

The second is the surface tension of water, which increases the pressure required to form a bubble. If the bottom surface is perfectly smooth, nucleation of bubbles is difficult, and the onset of boiling can be delayed to higher temperatures as water remains in a metastable liquid state.

Note that when boiling water you will often see bubbles form at an early stage and then disappear as the temperature increases : those bubbles are not water vapor but dissolved gases. Sign up to join this community. The best answers are voted up and rise to the top.

Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. Why do liquids boil when their vapor pressure equals the ambient pressure?

Ask Question. After your experiment, evaluate your results. Was your initial guess correct? Why or why not? As long as you're experimenting with boiling water, you might as well put it to good use. If you've got some eggs, cheese, and toothpicks, you can create a tasty treat right in your own kitchen. Read through the recipe for Hard Boiled Egg Boats and have fun cooking together as a family! Did you get it? Test your knowledge. Wonder Words barn grub pot soap float solid pasture placid steamy familiar molecule altitude conversation cauldron chemical dissolved gaseous atmospheric Take the Wonder Word Challenge.

Join the Discussion. Farhan Nov 2, I have been wondering what the reason for this everyday phenomenon is? Nov 4, You're welcome, Farhan! Josie 5th grade Dec 2, I am a goofy funny tech guru!

I was "wondering" if you could make another wonder on technology!! Maybe make one apposing to what wifi is or something else? Dec 2, Gas level increases the size of the bubble I think. Nov 21, That sounds about right, ! Bigger bubbles have more gas in them! Bella Mrs. Thompson Class Nov 2, Thought:I did not know that the bubbles in boiling water are actually water in a different physical state.

Connection: I just boiled water for mac-n-cheese today. Prediction: I predict the next wonder will be why can't we see germs. Nov 3, Thanks for sharing what you learned with us, Bella!

We hope you enjoyed your mac and cheese! We're glad you joined the conversation, vada! I think the heat goes up and makes the bubbles. Nov 1, Thanks for sharing your thoughts, sam. We hope you enjoyed exploring this Wonder! Oct 31, Alanna Oct 27, Oct 28, It's great that you learned some new things, Alanna! Rebecca Oct 26, Oct 27, Valerie Oct 26, Isn't it fun to learn new things, Valerie?! Oct 26, May 14, Hi, potato! In an open system this is called atmospheric pressure.

The greater the pressure, the more energy required for liquids to boil, and the higher the boiling point. In an open system this can be visualized as air molecules colliding with the surface of the liquid and creating pressure. This pressure is transmitted throughout the liquid and makes it more difficult for bubbles to form and for boiling to take place. If the pressure is reduced, the liquid requires less energy to change to a gaseous phase, and boiling occurs at a lower temperature.

Video: Atmospheric Pressure and Boiling www. Based on the atmospheric pressure, predict the boiling point for water at the following locations. Assume constant temperature. The boiling point on Mt. The molecules leaving a liquid through evaporation create an upward pressure as they collide with air molecules. This upward push is called the vapor pressure. Different substances have different vapor pressures and therefore different boiling points.

This is due to differing intermolecular forces between molecules. Video: Vapor Pressure and Bioling youtu. The vapor pressure of a liquid lowers the amount of pressure exerted on the liquid by the atmosphere. As a result, liquids with high vapor pressures have lower boiling points.