Question

The internal energy value is ____________ that the enthalpy value

A) smaller or equal

B) lager or equal
C) can be equal ,smaller or larger

Answer 1

Mathematically,

H = U + PV

where H is enthalpy

U is internal energy

PV is work done on or by the system

PV, work done is considered as positive when it is done by the system n atmosphere for example in the expansion process. It is considered as negative when the work is done over the system by an external application for example in contraction.

Internal energy is the sum of kinetic energy, potential energy, chemical energy and physical energy possessed by the system regardless of its macroscopic motion.

Enthalpy is the amount of heat content used or released in a system at constant pressure.

Now, the enthalpy is lesser than internal energy in contraction process

It can be equal to internal energy when there is no net change of volume when a process is done at constant pressure. for example in increasing the temperature of water without changing its phase.

and enthalpy is greater than internal energy when gas expands when supplied with heat.

Thus it can be concluded that the internal energy value can be equal, smaller or larger than enthalpy value.