Enthalpy at Constant Pressure

[eduardomorales5]

Is enthalpy at constant pressure mean that the system has to be at 1.0atm and 25 degrees celsius? Or is it simply that it should be at 25 degrees celsius?

[AArmellini_1I]

I believe it just means that its a closed system (like a piston) so while volume may change the pressure will never change because the system can expand and contract

[Qiu Ya Wu 4I]

Enthalpy at constant pressure is referring to essentially an open system with an air pressure of 1.0 atm. With an open system, the gas has the ability to push the air on top of the beaker out of the way, therefore performing work onto it.