The change in atmosphere is almost immediately discernible between chapters fourteen and fifteen of To Kill a Mockingbird by Harper Lee. It is not that we didn't feel the change coming, but we were not certain when it would happen. Chapter fifteen is when the trial for which the Finch family has been taking so much grief finally becomes a reality.
The basic plot of this chapter includes a rather odd meting on the Finch lawn, Tom Robinson moving to the Maycomb County jail the next day, Atticus going out unexpectedly at night, the three kids following him, and ending with the (what turned out to be) peaceful confrontation outside the jail. All of these events lead to the trial which begins in the next chapter. We can see chapter fifteen as a kind of transition, chapter, then. Because of that, it demonstrates some of the same atmosphere (most notably of innocence) as the first part of the novel, but it also introduces some new elements, such as fear and suspicion.
In an essay about the language in this chapter of the novel, all of those elements should be addressed: childlike innocence, fear, and suspicion. One organizational strategy for an essay, then, is to give examples of the language Lee uses to create these elements in the atmosphere. For example, Scout "burst[s] into the circle of light" at the jail, and we feel her innocence. The men "murmur," indicating something suspicious, and the prison is ominously described as "venerable and hideous," adding to an atmosphere of fear.
In a broader sense, language could include dialogue, and of course there are all kinds of examples of these three emotions in the dialogue in this chapter. For example, Scout's innocent question
“Hey, Mr. Cunningham. How’s your entailment gettin‘ along?”
reminds us both of her naivete and a more innocent time in the story. In the same scene, fear is palpable when Atticus realizes the danger his children are in. His terse and repeated order to Jem to "Go home" is like nothing we have heard from the reasonable father, a sure sign of his fear. Aunt Alexandra's overheard comments and the whispers of conversation on Atticus's front lawn are also clear indicators of fear. We recognize suspicion when Jem asks Atticus about the men on the lawn:
“It wasn’t a—a gang?”
The suspicion comes mostly from the kids because there is so much going on that they do not understand.
Another component of language is the use of details to create these this transitional atmosphere. For example, Jem's "foolproof plan to make Boo Radley come out" is to leave a trail of lemon drops creates a childlike atmosphere. The whispers of the men on the front lawn create suspicion, and the ominous image of Atticus sitting under the dim light of the jailhouse when four dusty cars appear and the men inside them get out creates a sense of fear.
One clear organizational strategy for this essay, then, might be to discuss these three key emotions (or any others you might want to include) which are used to create atmosphere and how they are portrayed through language. Depending on how you have been instructed to define "language," you might also include three language strategies (such as description, dialogue, and details) to explain how Lee creates the atmosphere in this chapter. Perhaps you are not allowed to do this, but it might be interesting to examine how Lee's use of language in this chapter differs from how she uses it in other chapters (primarily the addition of fear and suspicion).