Why does enthalpy H=U+PV look the same as the first law equation?

[asdf1]

in my thermodynamics textbook, enthalphy=U+PV
and (delta)heat=(delta)U+(delta)PV
those 2 look the same...
can anybody explain the difference?
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[Q_Goest]

Hi asdf1. Take a look at your book again, I think you've taken it out of context. For example, flow through a pipe where heat is added or removed between two points in the pipe is a process in which the heat added/removed is equal to the enthalpy change in the fluid. On the other hand, for the situation where heat is added to a sealed container (ex: a pressurized tank), the amount of heat added or removed is equal to the change in the fluid's internal energy.

 

[hotvette]

I was taught that enthalpy was a property of a substance. Heat is a transport phenomenon only (i.e. transfer of energy) and that there is no such property as heat.

 

[GCT]

at constant pressure with only expansion work the enthalpy of the substance does equal to the heat pertaining to the situation, that is $$q_p$$

 

[asdf1]

thanks! :)