The reaction between butanoic acid and ethanol is:
CH3CH2CH2COOH + CH3CH2OH → CH3CH2CH2COOCH3CH2 + H2O
Based on the reaction stoichiometry:
1 mole of butanoic acid forms 1 mole of ethyl butyrate
Now,
Molar mass of Butanoic acid = 88.0 g/mol
Given mass of butanoic acid = 7.20 g
Therefore, # moles of butanoic acid reacted = 7.20/88.0 = 0.0818 moles
# moles of ethyl butyrate formed = 0.0818 moles
Molar mass of ethyl butyrate = 116 g/mol
Mass of ethyl butyrate synthesized = 0.0818 * 116 = 9.49 g