Chem 115 Past Exams

What You Need to Know About Using Chem 115 Past Exams Effectively

I spent three semesters grading Chem 115 midterms before I figured out how students actually use past exams, and honestly, most of them use them wrong. They print everything, highlight half the pages, and then panic when the real exam looks different. The gap between what Chem 115 Past Exams can do for you and what they actually do is wider than most people realize. First, the practical stuff. You get these from the department office or the student union noticeboard. Sometimes they're scanned PDFs from 2018, sometimes they're actual paper copies with coffee stains on them. The formatting is inconsistent because different TAs wrote them over different years. That inconsistency matters more than you'd think, because it tells you which topics rotate and which ones are stable. Here's the method that actually works. Pick two exams from consecutive years — not the most recent one, because those get recycled too aggressively. Work through them under timed conditions with nothing open except the periodic table your instructor allows. Then grade yourself using whatever answer key exists. If there's no key, compare your answers against a classmate's and work out the disagreements. The disagreement part is where you learn.

I ran into a specific problem last year that I still think about. The 2019 midterm had a question on Hess's Law that asked students to calculate enthalpy for a reaction where one of the intermediate steps wasn't balanced. The 2021 version of the same question had the exact same setup but with different compounds, and students who had only memorized the steps from the 2019 exam got it wrong because they applied the same coefficients blindly. I've seen this pattern repeat every time a TA tries to refresh a question by swapping in new chemicals without checking whether the stoichiometry still works cleanly. My workaround was simple: for every thermochemistry question, I rewrite the entire cycle from scratch instead of plugging numbers into a template. It takes longer but it catches those traps.

Where Chem 115 Past Exams Fall Short

They don't cover the conceptual questions that show up when the professor decides to be creative. Past exams are reliable for computational problems — stoichiometry, gas laws, equilibrium calculations — because those tend to stay mechanically similar year to year. But the multiple choice sections on molecular geometry or bond theory can shift dramatically depending on which textbook chapter the professor emphasizes that semester. I've watched students who aced every past exam question on VSEPR bomb the actual midterm because the professor had switched to a different diagram style for electron domain counting. Another limitation: the difficulty curve isn't consistent. Some years the exam is straightforward — plug the formula, get the answer. Other years the questions are deliberately multi-step in ways that past exams from easy years don't prepare you for. The 2020 midterm, for example, combined acid-base equilibria with solubility product calculations in a single problem, and that combination had never appeared in any previous year's paper. If you only practice with the older exams, you'll be caught off guard by that kind of synthesis question. The answer keys, when they exist, are often incomplete. You'll find the final numerical answer but not the work, which means you can't tell whether you got the right number for the right reason or through some accidental cancellation. I always cross-reference my work with the solution manual from the textbook the course uses, or I ask a TA during office hours to walk through one or two problems I'm unsure about. Office hours are underutilized for this purpose, and it's a waste.

One thing that surprises people: doing all the past exams isn't better than doing the right ones. Working through six exams carefully, understanding every mistake, is worth more than skimming twelve. I've seen students accumulate forty pages of highlighted past exams and still miss the same type of error on the final. The error usually traces back to not understanding why a particular sign convention matters in thermodynamics or how to handle significant figures when the question involves subtraction of similar-magnitude values. If your instructor posts practice problems on Canvas or the course portal, those are sometimes more representative than the archived past exams, because they reflect the current year's pacing and emphasis. Use both. Start with the practice problems to calibrate what's in scope, then move to the past exams for stamina and timing. The biggest practical tip I can offer is this: keep a mistake log. When you work through a past exam and get something wrong, write down the question, your incorrect approach, and the correct approach in one place. Not the whole solution — just enough that next time you see a similar setup you'll catch yourself before making the same error. I used a simple three-column table in a notebook. It sounds tedious, but it cuts down repeat mistakes by half, usually within two weeks of consistent use.

You can usually find the actual files at the chemistry department's resource page or the student-run study group's shared drive. Some semesters the materials disappear mid-term because the professor updates the exam bank, so grab everything while it's available. I've lost access to a full set of past exams three days before a midterm because the link expired, and that's not a situation you want to be in.