1. The problem statement, all variables and given/known data The state of 3.75mol ideal gas changed from 0.3atm and 500K to 2.2atm and 330K under constant external pressure (Pex = 2.2atm). Calculate ΔE, work (w) and heat(Q), ΔH, ΔS. 2. Relevant equations w= -∫PexdV ΔE=1.5nRΔT=w+Q ΔH=ΔE+Δ(PV) ΔS=dQrev/T 3. The attempt at a solution I recently started a thermodynamics course and this question seems entry-level but I'm still unable to grasp some fundamental concepts. Calculating the energy change, work and heat was pretty straight forward: I used the appropriate equations to find energy change and work and then used the first law to find the heat. Problem is when I was asked about the enthalpy change, I thought "ok, this is a constant pressure proccess, so the enthalpy change is equal to the heat". But apparently this is not the case. What am I missing?