kinetic and potential energy of molecule....

[albertlee]

below is what I discovered..

 

If you heat up the water up to 100c, ie, it is boiling, the temperature no longer rises further...

 

I know the reason can be explained on the kinetic and potential energy of water molecules, but I just dont know how...

 

any body??

 

thx

[Xyph]

At that point the energy you supply starts being used to facilitate a state change (liquid to gas) rather than to raise the temperature. The same thing happens if you heat ice to 0 degrees, and at the melting and boiling points of all other substances. The kinetic energy is becoming sufficient to allow molecules to escape the intermolecular bonds holding the water in a liquid state rather than just making them move around more within the liquid.

[albertlee]

can any one from the below idea??

 

my teacher told me that the temperature indicates the magnitude of kinetic energy....

 

so if kinetic energy remains the same for molecules from luquid to gas state...

 

what does the other energy go to?

 

potential energy!!

 

but how?? what is the potential??

 

plz help

 

thx

 

ps, thx for response from Xyph

[Xyph]

Potential energy is energy gained from position. Any given object will have more potential energy the further it is from any given source of gravity, the more massive it is, and the stronger the given gravity well is - for example, an object suspended in the upper atmosphere will have more potential energy than one suspended at a few feet from the surface of the Earth, and, in each case, its potential energy will be converted into kinetic energy as it falls. The higher object will have more potential energy originally, and therefore will fall further, eventually gaining more kinetic energy than the lower object.

 

You can work out the potential energy of an object with the formula PE = mgh, where m is the mass, g is the gravitational acceleration (9.81~ in the case of Earth), and h is the height from the source of this gravitational acceleration (the surface of the Earth, for example).

[Primarygun]

I know the reason can be explained on the kinetic and potential energy of water molecules, but I just dont know how...

At 100 degree Celsius, energy supplied by heater is used for breaking the bonds(incresing potential energy) instead of giving velocity of molecules(KE)

[jdurg]

Breaking the intermolecular bonds, not the intramolecular bonds. (I.E. breaking apart the attraction each water molecule has towards the other water molecules. Not breaking apart the attraction between the hydrogen and oxygen atoms that make up the water molecule).

[[Tycho?]]

At 100 degree Celsius, energy supplied by heater is used for breaking the bonds(incresing potential energy) instead of giving velocity of molecules(KE)

 

Boiling water breaks no chemical bonds.

[albertlee]

Breaking the intermolecular bonds, not the intramolecular bonds. (I.E. breaking apart the attraction each water molecule has towards the other water molecules. Not breaking apart the attraction between the hydrogen and oxygen atoms that make up the water molecule).

 

but, doesn't breaking the intermolecular bonds involve mainly the more violent movement of molecules, hence the kinetic energy??

[Xyph]

Yes, if I interpret your question correctly. The more kinetic energy, the easier it is to break intermolecular bonds.

[albertlee]

yes, but the temperature should rise as more kinetic energy...,but, the during the melt/boiling, the temperature stays the same..implying the kinetic energy remains constant...

 

I am much focussing on the illustration of how do the molecules undergo the increase of potential energy...

 

any help??

thx

[Xyph]

As a molecule moves away from a source of gravity, it is using kinetic energy (upwards motion) to fight the gravity pulling it back. This kinetic energy is becoming potential energy. If the molecule starts falling again, it begins to lose potential energy, which becomes kinetic energy (as the falling motion).

 

 

As kinetic energy increases, generally, temperature increases, because the molecules are moving around more. Eventually, the movement of the molecules will be enough to break the intermolecular bonds holding them as a solid or a liquid.

 

The kinetic energy at this point is still increasing, but the temperature is not, because the molecules are not moving around any faster - they are just using the kinetic energy to break the intermolecular bonds, and the substance beings to melt, or boil.

[J.C.MacSwell]

yes' date=' but the temperature should rise as more kinetic energy...,but, the during the melt/boiling, the temperature stays the same..implying the kinetic energy remains constant...

 

I am much focussing on the illustration of how do the molecules undergo the increase of potential energy...

 

any help??

thx[/quote']

 

In boiling the average kinetic energy of the molecules in the liquid remain the same. Any excess tends to cause the higher speed molecules to "escape" as gas and the excess KE is carried of with them and/or converted to potential during the transition.

[albertlee]

so, in atomic theory, the potential energy is the same as the potential energy of energy due to gravity??

[J.C.MacSwell]

so, in atomic theory, the potential energy is the same as the potential energy of energy due to gravity??

 

Different fields.

[albertlee]

I think I get it,,

 

below is my explantation..

 

During evaporation, the molecules have reached a magnitude of kinetic energy enough to break their intermolecular bonds...

 

the kinetic energy is increasing, but the movement remains constant... it is pulling two molecules apart, and the longer the two molecules apart is, before breaking such bond, the more potential energy..

 

 

Ok.. another question.. what happens to the intermolecular bonds.. when the temperature is increasing??

[Xyph]

The higher the temperature becomes, the more strained they get, presumably, until they finally "snap" at the melting/boiling point.

[albertlee]

oh..

 

this strikes my understanding again....

 

if the more strained the molecules get, shouldn't the movement decrease??

 

Maybe an animation will illustrate it better??

[Xyph]

The movement won't decrease because it's the movement that is causing the strain in the first place.

[albertlee]

but why when breaking the bond, the movement stays constant??

 

how can you explain this during the melting of ice??

 

you say the energy is used to break the bond...but how does that explain the movement is constant??