Enthalpy formula from day 1

[Anika_Patel_1G]

Why does delta H = qp at constant pressure? I know we were told to memorize this, but I don't understand where it came from.

[Cynthia Tsang]

Because the pressure is not changing, none of the heat being released is going into the surroundings. This would make the change a closed system and all of the heat released in a reaction would equal the enthalpy of the reaction.

[Sirajbir Sodhi 2K]

I'm pretty sure enthalpy is really just a convention created by scientists to make calculations convenient (most reactions occur at constant pressure). It is really hard to explain the equations related to enthalpy from a conceptual standpoint. This one can be derived, but it requires the First Law of Thermo and some relatively difficult math.