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I'm current taking 2 thermo classes, engineering and chemistry, and I'm having trouble with the concept of enthalpy.

This is what I believe I understand. I Hope the following is all correct if not please correct me.

**H= U + PV**

The heat exchanged in a closed system under constant pressure is equal to

**(delta)H= q(for constant pressure).**Which would make (delta)H's physical interpretation the heat added or lost to the system under constant pressure.

The heat exchanged in closed system under constant volume is equal to

**(delta)U=q(for constant volume)**meaning the heat added or lost to the system under constant volume is equal to the change in internal energy

**Now to the actual question does enthalpy have a physical meaning in this particular scenario?**

Under a closed system in which

**pressure**and

**volume**are

**not constant**

the change in enthalpy would be

**(delta)H= (delta)U + delta(PV)**

which would make

**(delta)H= (delta)U + V(delta)(P) +P(delta)(V)**

However

**V(delta)P**seems to not have a physical meaning either. But if you subtract that term from both sides you get

(

**delta)H-V(delta)P=deltaU+P(delta)V**which I believe would equal this

**(delta)q=(delta)U+P(delta)V**

so is

**V(delta)P**just a correction term to obtain the heat from the change in enthalpy? or do both of them actually have a physical meaning?

Thanks in advance for any help