An ideal gas undergoes an isothermal expansion at 77ºC increasing its volume from 1.3 to 3.4 L. The entropy change of the gas is 24 J/K. How many moles o0f gas are present?

To obtain the number of moles n are present in the gas, substitute 24 J/K for ΔS, 8.31 J/mol. K for R, 3.4 L for V_f and 1.3 L for V_i in the equation,
n = ΔS/ (R ln V_f/V_i)
= (24 J/K) / (8.31 J/mol. K) (ln 3.4 L/1.3 L)
= (24 J/K) / (8.31 J/mol. K) (ln (3.4/1.3))
= 3.00 mol
From the above observation we conclude that, the number of moles n are present in the gas would be 3.00 mol.