Would it be possible to run KDE on a root partition of 16 GB, a Home partition of 25GB and a Swap partition of 8GB and 2 GB ram?

Yes
- 16gb should be fine for Root (I have 20gb but use only 14gb ), this is dependent on things like packages installed and log and crash files not being removed. Depending what you install less will work but 16 should be safe.
- 25gb Home is only an issue if you need more to store documents/music/videos/etc....
- I use a swap of 5gb because it's needed to hibernate else 2 should be fine, the old rule of thumb was twice physical ram but 2gb should be fine (1 even) note is is possible to add swap space latter by using a special swap file.

This is good to know. I've got an old laptop lying around and was wondering if it could run it. It's pretty old and even back then it wasn't a powerhouse but it looks like it'll be fine.