How does the mood change in chapter to generate several words to describe the mood in the story in the beginning and at the end of the chapter what causes the change

At the beginning of the chapter, George and Lennie are simply happy to have arrived... even if they're late. The conditions of their room.... the bug killer, gets an immediate reaction out of George. Their later meeting with the boss does the same. George takes umbrage at the boss' questions, Curley succeeds in bullying Lennie, and the appearance of Curley's wife sets off alarm bells. The mood is filled with tension.