Question

what are antibiotics why do antibiotics work against bacteria but these are not effective for viral disease

Answer 1

Let's look at two of the common ways antibiotics work. (Others exist, but the principles are similar)

1-  inhibit the synthesis of the cell wall. Most (not quite all) bacteria have cell walls. The antibiotic prevents them from making it, and water comes into the cell by osmosis it pops (Lyse) because the cell wall isn't there to hold it in. (Yes you can get bacteria to live in that antibiotic without a cell wall if you balance the osmosis in a lab, but this doesn't apply to infections).  These drugs are usually not too toxic to us (some exceptions), because we don't have cell walls anyway. The point is that viruses simply do not have cell walls. Therefore they are not affected by let's say penicillin and similar drugs.

2- several antibiotics affect the bacterias' ribosome.(sometimes called 70s)this inhibits protein synthesis. We survive  because our cells' ribosomes (80s) are not badly affected by these drugs. Our mitochondria do have 70s ribosomes, but we can tolerate the effect better than bacteria do. (Erythromycin, tetracycline, streptomycin are examples). Viruses simply use our ribosomes to make their proteins, so they are not affected any more than we are.

3- a drug that is related to antibiotics (technically not one) is sulfa drugs. They work by inhibiting folic acid synthesis. We don't mind because we eat it instead of making it anyway. Viruses don't make it, so they don't care either. (Anthropomorphizing, I know)

@AarushAgarwal

Answer 2

antibiotics are the chemical formed against the diseases in our body they help in providing strength against the disease if we take antibiotics when not needed they will less affective for next disease