I have seen the film Breathe In. In it Sophie (Felicity Jones) plays Chopin, but which piece? No reviews I have read mention this, and it doesn't seem to appear credited on IMDb. In reply to my question there @Emma_Diaz replies Ballade no. 2 in F Major, op. 38. Actually it is a bit of irony on the part of Sophie that went over my head as she refers to it as a student or warm up piece, I think. Whereas it is described as "one of the pinnacles of piano writing, [where] Chopin's 4 Ballades encompass everything that is great about the romantic period and display his total and complete genius, and affinity for the instrument."