Question

why the value of ∆H and ∆U are 0 ( zero) in ideal gas??

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Answer 1

Ideal gases:
So for isothermal process in which temperature remains constant.
dT=O.
So 
dU=O.

The internal energy of an ideal gas can be written as a function that depends only on the temperature.

so dU=0

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

Answer 2

It is not generally true that ΔU=0ΔU=0 in an isothermal process.

An ideal gas by definition has no interactions between particles, no intermolecular forces, so pressre change at constant temperature does not change internal energy.

Real gases have intermolecular interactions, attractions between molecules at low pressure and repulsion at high pressure. Their internal energy changes with change in pressure, even if temperature is constant.

For an ideal gas, in an isothermal process, ΔU=0=Q−WΔU=0=Q−W, so Q=WQ=W.