Belen is right, They are synonyms. Perhaps the only difference is that We tend to think of "Trozo" as an asymmetric piece or form of any material and "Pieza" as a symmetric piece or form of any material. I hope It helps.

Son sinónimos. La diferencia que a mi parecer veo, es que "trozo" es algo más coloquial. Y "pedazo" sería más formal.

I don't know in Spain but in Argentina they are synonyms.

Significa lo mismo. En España "trozo" se considera más formal, culto o educado que decir "pedazo"