Chemical Engineering Intern Interview Questions: Processes, Safety and Labs

Chemical engineering intern interviews at refineries, chemical and pharmaceutical plants, food and consumer goods makers and specialty materials companies are usually conversational, but they check three things: that you can do a mass and energy balance, that you understand unit operations at a practical level, and that you take process safety seriously. Expect questions about lab and plant experience, the software you have used, and how you would troubleshoot a unit that is running off specification. This page covers the rounds to expect, the questions that come up with what a strong answer contains, two sample answers, what interviewers expect from an intern, the mistakes that cost offers, and a two-week prep plan.

What the chemical engineering intern interview looks like

Questions that come up, and what strong answers contain

1. Walk me through a mass balance on a mixing or separation unit. Draw the boundary, list the streams and components, state the assumptions (steady state, no reaction), write accumulation equals in minus out plus generation minus consumption, and solve. Interviewers often give simple numbers to do on paper.
2. How does a distillation column work, and what would you check if the top product is off-spec? Separation by relative volatility, with reflux and boil-up. Check the reflux ratio, the feed composition and location, tray or packing problems such as flooding or weeping, and the instrument readings before changing anything.
3. What is a HAZOP? A structured team review that takes each node of a process on the P&IDs and applies guide words such as no, more, less and reverse to parameters such as flow, pressure and temperature, to find deviations, their causes and consequences, and whether the safeguards are adequate. It is one of the process hazard analysis methods listed in OSHA's Process Safety Management standard, 29 CFR 1910.119.
4. Why might a centrifugal pump cavitate? The net positive suction head available falls below what the pump requires, so vapour bubbles form and collapse. Causes include a low suction level, a hot fluid or a blocked suction strainer.
5. How is a heat exchanger sized? Q = U × A × ΔT_lm: the duty from the energy balance, an overall heat transfer coefficient and the log mean temperature difference, with a note on fouling and on counter-current versus co-current flow.
6. During a plant walk you see a valve that doesn't match the drawing. What do you do? Leave it alone and tell your supervisor or the area engineer. Mismatches between the field and the drawings are exactly what process safety information and management of change are meant to catch.
7. Tell me about a lab experiment that didn't go to plan. What you expected, what happened, how you checked your measurements and method, and what you changed.

Two sample answers

Walk me through a mass balance.

Say a mixer takes 100 kilograms an hour of a 20 percent salt solution and 50 kilograms an hour of pure water. At steady state with no reaction, total mass in equals mass out, so the product is 150 kilograms an hour. For salt, 20 kilograms an hour comes in, so the product is 20 over 150, about 13.3 percent. I always do the component balance as well as the total, because it catches mistakes, and I state the steady-state assumption out loud.

Tell me about a lab experiment that went wrong.

In our unit operations lab, the heat exchanger data gave an overall heat transfer coefficient about 40 percent below the range we expected. Rather than blame fouling, we checked the thermocouples against a reference thermometer and found one outlet sensor reading three degrees high. After correcting for it, the value fell within range. I learned to validate instruments before trusting a calculation built on them.

What interviewers expect from an intern

• Fundamentals you can apply: balances, thermodynamics, heat transfer, separations and kinetics.
• A safety mindset: knowing what process safety management, HAZOP and management of change are for.
• Software and data skills: Excel, and any process simulator you have used, such as Aspen Plus or HYSYS, tied to something you built.
• Hands-on evidence from labs, research or a previous internship.

For a neighbouring engineering internship, see mechanical engineering intern interview questions.

Mistakes that cost offers

• Treating safety questions as box-ticking.
• Listing a simulator without being able to describe a flowsheet you built in it.
• Changing several variables at once in a troubleshooting answer.
• Not knowing what the plant you would work at actually makes.

A two-week prep plan

1. Days 1 to 3: mass and energy balances by hand, with and without reaction, including one recycle stream.
2. Days 4 to 6: unit operations: distillation, heat exchangers, pumps and reactors, each with one troubleshooting scenario.
3. Days 7 to 8: process safety: read the headings of OSHA's PSM standard (process hazard analysis, operating procedures, mechanical integrity, management of change, incident investigation) and learn the HAZOP method.
4. Days 9 to 10: prepare two project stories from labs or research with data, what went wrong and what you learned.
5. Days 11 to 14: research the company's sites and products, compare our manufacturing engineer interview questions for plant roles, prepare your questions and run two mock interviews.

Timing matters as much as preparation: see our internship recruiting timeline, and once you are in, turning an internship into a return offer. Before the last round, prepare your questions to ask at the end of an intern interview.

Where CoPilot Interview fits

Intern interviews reward clear explanations of your own projects and coursework, and that takes practice out loud. CoPilot Interview is an AI interview assistant; its free AI mock interview builds chemical engineering intern questions from your résumé and the job description, reads them aloud, scores each spoken answer out of ten and shows a model answer to compare. The free plan gives 15 minutes a day of live help in sessions of up to 15 minutes, with AI mock interviews included, with no card, which suits a student budget. For real interviews and online assessments, follow your employer's rules.

Disclosure: CoPilot Interview is our product, so weigh what we say about it accordingly.

Frequently asked questions

Do chemical engineering interns need to know Aspen?

It helps but is rarely required. If you used Aspen Plus or HYSYS in a design course, be ready to explain a flowsheet you built and how you checked it; if not, say what you expect to learn.

Should I take the FE exam before a chemical engineering internship?

It isn't expected. Many students take it near graduation. NCEES offers a Chemical discipline FE exam with 110 questions, computer-based at Pearson test centres year-round, with a $225 fee as listed on its site on November 12, 2026. Interviewers may ask about your licensure plans.

Are chemical engineering intern interviews technical?

Moderately. Expect a few fundamentals questions or a quick calculation, plus a lot of behavioral and safety discussion. Plants care as much about judgment and reliability as about textbook answers.

Can I use AI tools during an internship interview?

Only where the instructions allow it. Online assessments and many live rounds forbid outside help. Use AI to practice beforehand, and follow your employer's rules.