Why do i feel my stomach warm when drinking alcohol on empty stomach. but when i have eaten something i dont feel it warm. also there is no pain.

Faster absorption: Alcohol makes blood vessels become larger, or vasodilate, which can create a feeling of warmth. If you don't have any food in your stomach to absorb the alcohol with, you are more likely to feel the effects of just the alcohol alone. Having food in your stomach slows down the rate of absorption of the alcohol and therefore you wouldn't feel those effects quite as easily.