Question

Is chane in enthalpy zero for an isothermal process?

Answer 1

Change in internal energy = 0. And ifchange in PV is zero enthalpy changeis also zero. It appears that PV changeis zero for isothermal process, that is true only for ideal gases. For real gases, it is not so and thus for real gases there is a some enthalpy change when it undergoes anisothermal process.

• dH=dE+d(pV)______(not only pdV.)
• dH=dE+pdV+Vdp
• For the isothermal process dE=0
• And for using the ideal gas equation pV=mRT__________(1)
• Differentiating (1) with v we can write pdV=constant because T is constant
• And again differentiating equation (1) with p we can write Vdp=0
• So that last two terms are zero ,too.
• So that for ideal gas we can say that the enthalpy is zero