[Spasmodic]

i wonder why is sodium after reacted with chlorine becomes a highly exothermic reaction. How to relate the concept of net decrease of potential energy of ions after bonding to this?? i thought there is no release of energy. its just only the coulombic attraction between the two atoms? i still dont get why energy will be release like after bonding?  pls reply asap. thanks a million =)

[Yggdrasil]

Try to remember back to physics when you learned about work and energy.  If you do work on an object, you are giving the object energy.  So, when the electrostatic force brings two opposite charges together (i.e. decreasing the distance between the charges), the electrostatic force does work on the charges.  This work (since it is work done by an attractive force) decreases the potential energy of the charges (specifically their Coulombic potential).

[Spasmodic]

i kind of got what u meant. but, what kind of energy is that, potential energy? kinetic energy? radiation? still quite confusing. knock some sense into me.

[Yggdrasil]

It's potential energy.  Remember when your physics teachers said that potential energy is energy of position.  Here, the charges have a lower potential energy due to the fact that they are positioned closer to each other.

[wildstar]

See the Born-Haber Cycle:
http://en.wikipedia.org/wiki/Born_haber