Not to mention that it would be tremendously difficult for the average joe to do a processor replacement on a laptop.
If you don't know whether it will work, I am not sure that it is advisable for you to attempt what you are considering.
If you really wanted to pull something off like a processor switch, you would probably want to aim at something like an i5-2520m which is kinda more like an i3-2120 in reality, but at least it is designed to fit laptops.
However, I do want to re-iterate that you may want to opt not to do the project at all.
I am a veritable wizard when it comes to computer hardware and there isn't much at all that would intimidate me, but if I were thinking of doing what you are considering, I would be a bit intimidated.
I can't remember ever hearing of anyone pulling such a thing off, or even attempting it for that matter, and I hear a lot of stuff.
Most people generally consider laptops to be unupgradeable except possibly the RAM and hard drives. For good reason too.
If you have a warranty, I almost guarantee it would be voided by trying to replace a processor.
The heatsink for an i5-2500k would be too big to fit in a laptop even if the CPU has compatible socket. Basically you would need to cut an opening in your laptop so that the heatsink could protrude out from it. Generally speaking, that would destroy the laptop (again, assuming a desktop and laptop Sandy Bridge CPU used the same socket).
yes technically you can do it. i have seen hexacore i7s in laptops but these laptops are huge and expensive. if you bought a shelf laptop you have no chance in doing it without changing the motherboard and probably the power supply.