Chapter 6.2: Enthalpy: Changes at Constant Pressure

Flashcards from Chapter 6.1 of Chemistry: The Molecular Nature of Matter and Change.

Enthalpy (H)

A thermodynamic quantity defined as the sum of internal energy and the product of pressure and volume, at constant pressure, without any PV work

• H = E + PV

Change in enthalpy (Delta H)

The heat released or absorbed of a system at constant pressure

• Change is denoted as ΔH = ΔE + PΔV = q + w + PΔV

  • As w = -PΔV, this can be simplified to ΔH = q_P

  • Essentially equal to ΔE for most cases, given small or no changes in PΔV

• Sign determines whether heat is released or absorbed when examining energy

Heat at constant pressure (q_P)

The heat released or absorbed in a reaction specifically at constant pressure, equal to the change in energy

Enthalpy diagram

A diagram demonstrating the flow of energy in a enthalpy reaction