A sample of helium (He) gas initially at 23°C and 1.0 atm is expanded from 1.3 L to 3.1 L and simultaneously heated to 44°C. Calculate the entropy change for the process.

Respuesta :

Answer : The change in entropy is, 8.65 J/K

Explanation :

Formula used :

[tex]\Delta S=nC_v\ln (\frac{T_2}{T_1})+nR\ln (\frac{V_2}{V_1})[/tex]

where,

[tex]\Delta S[/tex] = change in entropy

n = number of moles of gas  = 1 mole

R = gas constant  = 8.314 J/mol.K

[tex]C_v[/tex] = specific heat capacity at constant volume = [tex]\frac{5}{2}R[/tex] (for monoatomic gas)

[tex]V_1[/tex] = initial volume of gas  = 1.3 L

[tex]V_2[/tex] = final volume of gas  = 3.1 L

[tex]T_1[/tex] = initial volume of gas  = [tex]23^oC=273+23=296K[/tex]

[tex]T_2[/tex] = final volume of gas  = [tex]44^oC=273+44=317K[/tex]

Now put all the given values in the above formula, we get:

[tex]\Delta S=1\times \frac{5}{2}R\ln (\frac{317}{296})+1\times R\ln (\frac{3.1}{1.3})[/tex]

[tex]\Delta S=1\times \frac{5}{2}\times 8.314\ln (\frac{317}{296})+1\times 8.314\ln (\frac{3.1}{1.3})[/tex]

[tex]\Delta S=8.65J/K[/tex]

Therefore, the change in entropy is, 8.65 J/K