Internal Energy!

[chocofingers]

hi,
Can anybody explain the phenomenon behind internal energy? and what is the change in internal energy when water evaporates. Please do give reference to first law of thermodynamics.
Thanks in advance.

[Hootenanny]

hi,
Can anybody explain the phenomenon behind internal energy? and what is the change in internal energy when water evaporates. Please do give reference to first law of thermodynamics.
Thanks in advance.
Welcome to Physics Forums.

Hyperphysics is generally a pretty good reference for elementary concepts in physics. Here are the appropriate links:

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/intengcon.html#c1
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/inteng.html
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/phase.html#c3

[chocofingers]

Thank you for the references.
here one of the references says that molecular attractive forces are associated with internal energies also. SO heating water means breaking potential energy bonds and hence decreasing potential energy of the system.thereby the internal energy of the system would reduce ???????

[Hootenanny]

Thank you for the references.
here one of the references says that molecular attractive forces are associated with internal energies also. SO heating water means breaking potential energy bonds and hence decreasing potential energy of the system.thereby the internal energy of the system would reduce ???????
No. In this case, the potential energy is a negative quantity, analogous to gravitational potential energy. Therefore, breaking molecular bonds increases the potential energy and hence increases the internal energy.

See the section entitled "Why is the Potential Energy Negative?" on this page: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/phase.html#c3

[chocofingers]

Thankyou sir! I was lingering over this topic since ages and got it NOW!
Thanks :)