Why didn't Hashem inform Moshe before each plague that Pharaoh would not listen to them?
Rashbam: Although the Torah only records it here, in fact, Hashem did indeed inform Moshe before each plague. 1
"Mofesai" is plural; which punishments is "Lema'an Revos Mofesai" referring to?
Rashi: It is referring to Makas Bechoros, Keri'as Yam-Suf, and the drowning of the Egyptians. 1
Ramban: It is referring to Makas Bechoros (which occurred before Pharaoh sent Yisrael away), and what Hashem meant was that He had hardened his heart against capitulating even in the face of Makas Bechoros - in order to perform multiple wonders (more than all the other plagues), by killing man, animals and destroying their gods in one fell sweep. 2