Calculate the internal energy and enthalpy changes resulting if air changes from an initial |state of 5°C and 10bar, where its molar volume is 2.312 x103 m?mol1, to a final state of 60°C and 1 bar. Assume also that air remains a gas for which PV/T is constant and that C 20.785 and Co 29.100 Jmol K

Respuesta :

Answer :  The change in internal energy and change in enthalpy of the gas is 1143.2 J/mol and 1600.5 J/mol respectively.

Explanation :  

(a) The formula used for change in internal energy of the gas is:

[tex]\Delta U=C_v\Delta T\\\\\Delta U=C_v(T_2-T_1)[/tex]

where,

[tex]\Delta U[/tex] = change in internal energy = ?

[tex]C_v[/tex] = heat capacity at constant volume = [tex]20.785J/mol.K[/tex]

[tex]T_1[/tex] = initial temperature = [tex]5^oC=273+5=278K[/tex]

[tex]T_2[/tex] = final temperature = [tex]60^oC=273+60=333K[/tex]

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

[tex]\Delta U=nC_v(T_2-T_1)[/tex]

[tex]\Delta U=(20.785J/mol.K)\times (333-278)K[/tex]

[tex]\Delta U=1143.175J/mol\approx 1143.2J/mol[/tex]

The change in internal energy of the gas is 1143.2 J/mol.

(b) The formula used for change in enthalpy of the gas is:

[tex]\Delta H=C_p\Delta T\\\\\Delta H=C_p(T_2-T_1)[/tex]

where,

[tex]\Delta H[/tex] = change in enthalpy = ?

[tex]C_p[/tex] = heat capacity at constant pressure = [tex]29.100J/mol.K[/tex]

[tex]T_1[/tex] = initial temperature = [tex]5^oC=273+5=278K[/tex]

[tex]T_2[/tex] = final temperature = [tex]60^oC=273+60=333K[/tex]

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

[tex]\Delta U=nC_v(T_2-T_1)[/tex]

[tex]\Delta U=(29.100J/mol.K)\times (333-278)K[/tex]

[tex]\Delta U=1600.5J/mol[/tex]

The change in enthalpy of the gas is 1600.5 J/mol.