1. The problem statement, all variables and given/known data State whether the thermodynamic quantities q (heat), w (work), ΔU (internal energy) and ΔS (entropy) are greater than, equal to, or less than zero when one mole of an ideal gas expands irreversibly and against a constant external pressure of zero. 2. Relevant equations Well, I know that ΔU = w + q, and w = PΔV. 3. The attempt at a solution As P = 0, w = 0. If the system was insulated, q would be equal to zero, but it doesn't say anything about that. I have no idea about ΔU or ΔS. I'm really struggling to understand thermochemistry!