Yes, when pressure is constant, the enthalpy change can still occur. Enthalpy (H) is defined as the sum of internal energy (U) and the product of pressure (P) and volume (V) for a system:
H = U + PV
If the pressure is constant (P = constant), any change in enthalpy is solely due to the change in internal energy. This means that the enthalpy change (ΔH) will be equal to the change in internal energy (ΔU).
ΔH = ΔU
So, while the pressure remains constant, the enthalpy can still change if there is a change in internal energy. This often occurs during chemical reactions or physical processes where heat is exchanged.