unbalance/imbalance

I. Are 'unbalance' and 'imbalance' interchangeable in the following?
1. create a greater unbalance/imbalance in the supply and demand of labor
2. a massive unbalance/imbalance of wealth between urban and rural areas
3. trade unbalance/imbalance
4. economic unbalance/imbalance

II. Is this understanding correct?
1. 'imbalance' is always a noun, never used as a verb
2. 'unbalance' is usually used as a verb, but when it
is used as a noun, it means either:
(a) mental disorder
or
(b) it is used in the technical field
e.g. If that rotor is not running in one of its critical speeds, then your problem is an unbalance problem we all face on a daily basis,....

Thank you.