The CW has released an official description of the the 7th episode of the season:

LANA ABSORBS CLARK’S POWERS AND GOES AFTER LEX — Kryptonite and high voltage mix during a lightning storm, causing Lana (Kristin Kreuk) to absorb Clark’s (Tom Welling) powers. Using her newfound super powers, she breaks into Lex’s (Michael Rosenbaum) safe and steals incriminating evidence which she then delivers to Lois (Erica Durance) and Grant (Michael Cassidy), demanding they run a story exposing Lex’s secrets. After Grant refuses to use stolen material, Lana decides to take care of Lex herself. Clark tries to stop Lana from killing Lex and a super battle ensues between the two. Allison Mack, Erica Durance, Aaron Ashmore and John Glover also star.

Neither Jimmy Olsen nor Kara appear in this episode.

I have to say, pretty much anything that focuses on Lana makes me want to not watch Smallville these days, so I’m really not very excited about this episode. I’m also kinda concerned with how easy it seems to be to give someone else Clark’s powers. How many times has this happened now? A few – and each time it seems to get easier to do.

Eventually you’re just going to be able to rub up against him and steal his abilities.