How does Iago show the emotion of Envy in Act 2?

Iago is jealous of Cassio's promotion to lieutenant; he wishes to have that post for himself. He also yearns for Desdemona and is thus envious of Othello for having her. Furthermore, for whatever reason, he believes Othello has slept with his wife Emilia and he plans revenge by planning to drive Othello mad with jealousy.