The product of the reaction of pentanoic acid with ethanol in the presence of a strong acid is ethyl pentanoate, an ester.

Here's the reaction:

CH₃(CH₂)₃COOH + CH₃CH₂OH ⇌ CH₃(CH₂)₃COOCH₂CH₃ + H₂O

Pentanoic acid + Ethanol ⇌ Ethyl pentanoate + Water

This reaction is an example of Fischer esterification. Here's how it works:

1. Protonation of the carboxylic acid: The strong acid protonates the carbonyl oxygen of pentanoic acid, making it more electrophilic.

2. Nucleophilic attack: The ethanol molecule acts as a nucleophile and attacks the electrophilic carbon of the carbonyl group.

3. Elimination of water: A proton is lost from the ethanol portion, and a water molecule is eliminated, forming the ester.

The reaction is reversible, but the presence of a strong acid and the removal of water (usually by distillation) drive the equilibrium towards the formation of the ester.