IB Chemistry command terms 2026: What they mean and how to respond correctly
IB Chemistry command terms are the action words used in exam questions to tell students exactly what type of response, level of detail, and reasoning the examiner expects. Terms such as state, identify, describe, explain, calculate, deduce, evaluate, analyse, and discuss each require a different approach, and misunderstanding them can cost marks even when the chemistry itself is correct. The command term, together with the mark allocation, also helps students judge how much to write and how to structure their answer.
This guide explains the most important IB Chemistry command terms and how to respond to each one effectively in exam conditions.
- Why understanding command terms is essential for scoring high in IB Chemistry
- State and identify in IB Chemistry: How much detail is expected
- Describe and explain in IB Chemistry: The key differences and how to answer each
- Calculate and deduce in IB Chemistry: What level of working is required
- Evaluate, analyse and discuss in IB Chemistry explained
- How command terms affect mark allocation in IB Chemistry papers
- Frequently asked questions
Why understanding command terms is essential for scoring high in IB Chemistry
The IBO command terms in Chemistry are not suggestions. They are precise instructions that define the marking criteria for every question on every paper. Examiners use mark schemes built directly around these terms, which means your answer is assessed not only on whether your chemistry is correct, but on whether you have addressed the right cognitive level.
A student who writes three detailed paragraphs in response to a “state” question is not earning extra credit. They are wasting time and risking clarity. Equally, a student who writes a single sentence in response to an “evaluate” question will lose marks regardless of how accurate that sentence is.
Drawing on years of experience at Times Edu, we have seen this pattern repeat itself across hundreds of mock exams. The students who break into the 6 and 7 bands are rarely the ones who know the most chemistry. They are the ones who know how to translate their knowledge into the exact format each command term demands.
>>> Read more: IB Chemistry books 2026: Complete guide for students and teachers
State and identify in IB Chemistry: How much detail is expected
“State” and “identify” are both Cognitive Level 1 command words in IB Chemistry [1], meaning they require brief, factual responses with no justification needed.
State asks you to give a specific name, value, or fact. The answer should be one sentence at most. If the question is “State the shape of a water molecule,” the correct response is simply “bent” or “V-shaped.” Any additional explanation about bond angles or lone pairs is unnecessary unless a separate command term asks for it.
Identify is similar but typically involves recognising something within data, a diagram, or a given scenario. For example, “Identify the limiting reagent in the following reaction” requires you to point to a specific item from the information given rather than recalling a memorised fact.
A common mistake we see is students adding explanations to “state” answers. This is not only unnecessary but can introduce errors that cost marks. Keep it short, direct, and precise.
| Command term | Cognitive level | Expected response length | Justification required? |
|---|---|---|---|
| State | 1 | One sentence or phrase | No |
| Identify | 1 | One sentence or phrase | No |
| Define | 1 | One precise sentence | No |
| Outline | 1-2 | Two to three sentences | Brief only |
>>> Read more: IB Chemistry Paper 1 vs Paper 2: Key Differences + Strategy for Score 7
Describe and explain in IB Chemistry: The key differences and how to answer each
This is one of the most frequently confused pairings in IB Chemistry, and getting it wrong consistently is one of the fastest ways to lose marks on Paper 2.
Describe asks you to give an account of what happens, without needing to say why. For example, “Describe the trend in electronegativity across Period 3” requires you to state that electronegativity increases from left to right. You do not need to explain the reason unless “explain” is also present in the question.
Explain requires you to go one level deeper. You must state what happens and then provide the chemical reason behind it, linking cause to effect. This is where the majority of marks are allocated in higher-difficulty questions on IB Chemistry Paper 2 command words.
One critical detail often overlooked is the logical connector. When writing an “explain” answer, examiners look for language that shows causation. Phrases like “because,” “therefore,” “which results in,” and “this means that” are not stylistic choices. They are the structural evidence that you understand the mechanism, not just the outcome.
Example comparison:
Describe question: “Describe the change in atomic radius across Period 3.”
- Correct response: “Atomic radius decreases from left to right across Period 3.”
Explain question: “Explain the decrease in atomic radius across Period 3.”
- Incorrect (Level 4 response): “It gets smaller because there are more protons.”
- Correct (Level 7 response): “The number of protons increases across the period, while the shielding effect from inner electrons remains approximately constant. The increased nuclear charge therefore exerts a stronger electrostatic attraction on the valence electrons, pulling the outer shell closer to the nucleus.”
The difference is not content. It is logical structure. Both students may know the same chemistry, but only one has used “describe explain IB Chemistry” correctly.
>>> Read more: IB Chemistry HL Mistake Log 2026: How to Track Errors and Turn Them into Score Improvements
Calculate and deduce in IB Chemistry: What level of working is required
These two terms both require active application of knowledge rather than recall, but they operate very differently.
Calculate is a Cognitive Level 2 command term that requires you to obtain a numerical answer with all working shown. Units must always be included in the final answer. Even if the final answer is wrong due to an arithmetic slip, examiners can award marks for correct methodology through “error carried forward” principles, but only if your working is visible.
For any “calculate” question, structure your response as follows:
- Write the formula or equation you are using
- Substitute the given values with units
- Show each conversion step (e.g., cm3 to dm3, grams to moles)
- State the final answer with correct units and appropriate significant figures
Deduce asks you to draw a logical conclusion from information provided in the question, such as a data table, a graph, or the IB Data Booklet. This term does not require prior memorisation in the same way. It requires you to read the available evidence and apply chemical reasoning.
For example: “Deduce the molecular geometry of SF4.” The question is signalling that you should use the electron domain geometry approach. You count 4 bonding pairs and 1 lone pair, determine the electron geometry is trigonal bipyramidal, and deduce the molecular geometry is seesaw.
In our experience working with international students, the most common error on “deduce” questions is answering from memory rather than from the data in front of them. If the question provides a graph or table, your deduction must be explicitly anchored to that data.
>>> Read more: IB Chemistry HL Study Plan for 2026: A Week-by-Week Schedule to Stay Ahead
Evaluate, analyse and discuss in IB Chemistry explained
These three command words represent the highest cognitive level in IB Chemistry. They appear most often in Paper 2 extended response questions and carry the greatest mark allocations. Students who master these terms are the ones who consistently achieve scores of 6 and 7.
Evaluate requires you to assess the strengths, limitations, or validity of something, whether it is a student’s experimental method, a set of data, or a claim. A complete evaluation must include a judgment that is supported by specific chemical evidence. It is not enough to list problems. You must say how those problems affect the outcome.
For example: “Evaluate a student’s method for determining enthalpy of combustion using a spirit burner.”
- Identify the flaw: Heat is lost to the surroundings rather than being fully absorbed by the water.
- State the effect: This causes the temperature change to be smaller than expected, leading to an enthalpy value that is less exothermic than the true value.
- Make a judgment: The method is unreliable for accurate thermochemical data without significant modifications such as using a bomb calorimeter.
Analyse asks you to break down information, data, or a process into its key components and examine how they relate. In IB Chemistry, this often involves interpreting graphs, spectroscopic data, or reaction mechanisms in detail. You need to identify patterns, explain what they mean chemically, and draw a conclusion.
Discuss is perhaps the broadest of the three. It requires a balanced treatment of a topic, covering multiple perspectives, arguments, or considerations. If a question asks you to “discuss the advantages and disadvantages of using hydrogen as a fuel,” a Level 7 response addresses both sides with chemical specificity, not vague generalities.
A common mistake we see in students’ “discuss” answers is presenting only one side of the argument. Examiners expect range. Even if you personally believe one position is stronger, you must engage with the counterargument.
| Command term | Cognitive level | Key requirement | Common mistake |
|---|---|---|---|
| Evaluate | 3 | Judgment with evidence | Listing flaws without stating impact |
| Analyse | 3 | Breakdown of components | Describing without linking cause and effect |
| Discuss | 3 | Balanced, multi-perspective response | Arguing only one side |
| Explain | 2-3 | Cause and effect reasoning | Writing what happens without saying why |
| Predict | 2 | Expected result based on trends | Predicting without referencing the trend |
>>> Read more: IB Chemistry: Syllabus, Exam Structure & Roadmap to an 7 in 2026
How command terms affect mark allocation in IB Chemistry papers
The mark allocation in every IB Chemistry question is directly calibrated to the command term used. A question worth one mark will almost always use “state,” “identify,” or “define.” A question worth four or five marks will use “explain,” “evaluate,” or “discuss.”
This connection between mark allocation and command terms gives you an immediate strategic tool during the exam. Before you write a single word, count the marks assigned to the question and cross-reference the command term. If you see four marks next to “explain,” you know the examiner expects at least four distinct, logically connected ideas.
One critical detail often overlooked by students is that IB mark schemes typically award one mark per correct, relevant point. For Cognitive Level 3 questions, those points must include both the chemical fact and the causal link. Writing “the boiling point is higher” earns zero marks on its own. Writing “the stronger intermolecular hydrogen bonds require more thermal energy to overcome, resulting in a higher boiling point” earns two marks because it contains both the cause and the effect.
Quick mark strategy by command term:
- 1-Mark questions: State, identify, define. One concise answer. No justification.
- 2-Mark questions: Often “outline” or “state and explain.” Give the fact and one brief reason.
- 3 To 4-mark questions: Usually “explain.” Three to four logically chained points using chemical reasoning.
- 5-Mark and above: “Evaluate,” “discuss,” “analyse.” Multi-part response covering range, evidence, and judgment.
The IB Chemistry Paper 2 command words are not random. They are a transparent signal of what the marking criteria requires. Students who learn to read them correctly can essentially reverse-engineer their way to a full-mark response before they write a word.
>>> Read more: IB Tutor 2026: How to Choose the Right Tutor for Better Grades and Less Stress
Frequently asked questions
What are the IB Chemistry command terms and why do they matter?
IB Chemistry command terms are the action verbs used in exam questions that define the type and depth of response required. Terms like “state,” “explain,” “evaluate,” and “deduce” each correspond to a different cognitive level and a different mark allocation structure. They matter because the IB marking criteria is built around these terms. An answer that ignores the command term, even if chemically accurate, will not earn full marks.
What is the difference between describe and explain in IB Chemistry?
“Describe” asks you to state what happens without providing the reason. “Explain” requires you to state what happens and provide the causal mechanism behind it. In practice, every “explain” answer should include a logical chain: The structural or atomic feature, the immediate physical consequence, and the final observable property. Using connecting language like “because” and “therefore” is essential for scoring full marks on explain questions.
What does deduce mean in IB Chemistry and how should you structure your answer?
“Deduce” means to draw a conclusion from evidence provided in the question, which may include data tables, graphs, or the IB Data Booklet. Your answer must explicitly reference that evidence rather than rely on memorised knowledge alone. Structure your response by identifying the key data point, applying the relevant chemical principle, and stating your conclusion clearly.
What does evaluate mean in IB Chemistry exam questions?
“Evaluate” requires you to assess the validity, strengths, and limitations of something, such as an experimental method, a conclusion, or a data set. A complete evaluation includes identifying specific flaws or strengths, explaining how they affect the data or outcome, and making a supported judgment. Listing problems without connecting them to their impact will not earn full marks.
What is the difference between state and outline in IB Chemistry?
“State” requires a single fact or brief answer with no explanation. “Outline” allows for slightly more detail, typically two to three sentences that give a summary of a process or concept without full mechanistic depth. The key distinction is that “outline” may involve naming steps or features in sequence, while “state” requires a single piece of information.
How do command terms affect how much you need to write in IB Chemistry?
The command term, combined with the mark allocation, determines your response length. A one-mark “state” question needs one sentence. A four-mark “explain” question needs four logically connected ideas, each containing a chemical cause and its effect. Writing too much for low-level command terms wastes time and can introduce errors. Writing too little for high-level terms costs marks directly.
Which IB Chemistry command terms appear most frequently in Paper 2?
Based on past paper analysis and the experience of our tutors at Times Edu, the most frequently appearing command words in IB Chemistry Paper 2 are “explain,” “calculate,” “deduce,” “state,” and “evaluate.” The extended response sections heavily favour “explain” and “evaluate,” making mastery of these two terms the single highest-impact study focus for students targeting a score of 6 or 7.
Conclusion
At Times Edu, our 1-on-1 IB Chemistry tutors work with students systematically on this skill from the very first session. If your child is preparing for IB Chemistry exams and is not yet consistently reading and responding to command terms at the right level, a personalised academic roadmap consultation can identify exactly where marks are being lost and how to recover them efficiently. Reach out to our team to get started.
