What the board asks
We went through the ISC board papers, question by question, and matched each question to a topic. Here is what was asked, how often, and what was never asked.
Chemistry: 384 topics in the 2027 syllabus, across 10 units. The board has asked 252 of them at least once. 132 were never asked in the papers we checked.
Pick a unit
C3 Chemical Kinetics
All the topics in Chemistry: Chemical Kinetics
Asked topics first, the most asked at the top. Tap a topic to see what to write, the result, the years, and the real board questions.
34 topics shown
| # | Topic | Type | Marks | Times asked | Last asked | Status |
|---|---|---|---|---|---|---|
| 1 | Order and rate law from initial-rate data tablePick two experiments where only one concentration changes, divide their rates to find the order in that reactant, repeat for the other reactant, then write the rate law and overall order (or pick the correct rate law from options). | Numericals | 3 | 5 papers | Specimen 2027 | Asked |
| 2 | First order: rate constant and time for x% completionFind k from given concentrations or a given percentage completed in a time using k = (2.303/t) log(a/(a-x)), then use the same k to find the time for another percentage, with units. | Numericals | 2 | 5 papers | Specimen 2027 | Asked |
| 3 | Activation energy from rates at two temperaturesWrite log(k2/k1) = (Ea/2.303R)(1/T1 - 1/T2), convert temperatures to kelvin, put in the ratio of rates or rate constants, and solve for Ea in kJ mol-1 (or find k at a third temperature given Ea). | Numericals | 2 | 5 papers | Specimen 2027 | Asked |
| 4 | First order: half-life, amount left, radioactive decayConvert between half-life and k, then find the fraction or percentage left after a time (by number of half-lives or by the log equation), or the age or time from the amount left, including word problems on radioactive isotopes. | Numericals | 2 | 4 papers | Specimen 2027 | Asked |
| 5 | Change in rate when concentrations are changedFrom the rate law, write the new rate as k times the new concentrations raised to their orders, divide by the old rate, and state the factor by which the rate changes. | Numericals | 1 | 4 papers | 2026 | Asked |
| 6 | Units of rate constant and order from unitsDerive the unit of k for a reaction of order n from rate = k[A]^n, and given a unit of k (s-1, mol L-1 s-1, mol-2 L2 s-1 ...) state the order. | Numericals | 1 | 4 papers | 2026 | Asked |
| 7 | Rate constant and new rate from initial-rate dataHaving the rate law, substitute one experiment's concentrations and rate to get k with its correct units, then use the rate law to calculate the rate at new concentrations. | Numericals | 1 | 3 papers | 2025 improvement | Asked |
| 8 | Overall order from a given rate law, including fractionalAdd the powers in the given rate law to give the overall order (it may be fractional, zero or involve a negative power) and state that order is found by experiment, not from the balanced equation. | Numericals | 1 | 2 papers | Specimen 2027 | Asked |
| 9 | Pseudo order when one reactant is in large excessFrom a rate law or a named reaction (acid hydrolysis of an ester, inversion of cane sugar), state the order when one reactant is in large excess and explain that its concentration stays nearly constant, while the molecularity stays the same. | Give reason | 1 | 2 papers | 2026 | Asked |
| 10 | Molecularity: meaning; order and molecularity of a reactionDefine molecularity as the number of particles colliding in one elementary step, and for a given reaction or rate law state its order and its molecularity. | Statement | 1 | 2 papers | 2026 | Asked |
| 11 | Characteristics of a first order reactionState the characteristics: k independent of initial concentration, unit of k is time-1, half-life independent of initial concentration, and give one example. | Statement | 1 | 2 papers | 2024 | Asked |
| 12 | Activation energy from half-lives at two temperaturesConvert each half-life to k with k = 0.693/t1/2 (or use k2/k1 = t1/2 at T1 / t1/2 at T2), then use the two-temperature Arrhenius equation to find Ea. | Numericals | 3 | 2 papers | 2023 | Asked |
| 13 | Arrhenius equation: symbols, log form, frequency factorWrite k = A e^(-Ea/RT), give the meaning of each symbol (A is the frequency or pre-exponential factor), and convert it to log10 k = log10 A - Ea/(2.303RT). | Statement | 1 | 2 papers | 2020 | Asked |
| 14 | Differences between order and molecularityGive the required number of differences in a two-column form: experimental vs theoretical, can be zero or fractional vs whole number only, for overall reaction vs for elementary step. | Comparison | 1 | 1 paper | 2025 | Asked |
| 15 | Arrhenius plot: Ea and A from log k vs 1/TSketch log k against 1/T as a straight line, state slope = -Ea/(2.303R) and intercept = log A, and calculate Ea (and A) from a given slope or intercept. | Graph | 1 | 1 paper | 2025 improvement | Asked |
| 16 | Threshold energy, activation energy and activated complexDefine threshold energy, activation energy (threshold energy minus average energy of reactants) and activated complex, and say why the activated complex is unstable. | Statement | 1 | 1 paper | 2023 | Asked |
| 17 | Show that: t75 = 2 x t50 and similar ratiosWrite t for each percentage with the first order equation, take the ratio, and show the result (for example t75/t50 = log 4 / log 2 = 2, t99.9 = 10 x t1/2). | Numericals | 2 | 1 paper | 2019 | Asked |
| 18 | Effect of a catalyst on activation energy and rateState that a catalyst gives an alternative path of lower Ea so more collisions are effective and rate rises, and that it does not change delta H, the equilibrium constant or the position of equilibrium, only the time to reach it. | Give reason | 1 | 1 paper | 2019 | Asked |
| 19 | Write the rate law; meaning of rate constantWrite the rate law for a reaction from given orders with respect to each reactant, define the specific rate constant k as the rate at unit concentrations, and state how rate and k differ. | Statement | 1 | 1 paper | 2018 | Asked |
| 20 | Slow and fast reactions explained by bonds brokenDefine chemical kinetics and its scope in one or two lines, then for each given reaction say whether it is fast or slow and give the reason in terms of bonds that must break (ionic reactions need no bond breaking, covalent reactions do). | Give reason | 1 | never | Never asked | |
| 21 | Rate of reaction: definition, units, average and instantaneousDefine rate of reaction, write its unit (mol L-1 s-1), and define average rate and instantaneous rate with the limiting form -d[R]/dt. | Statement | 1 | never | Never asked | |
| 22 | Rate in terms of each reactant and productFor a balanced equation, write the rate expression for every species divided by its coefficient, then use it to find the rate of disappearance or appearance of one species from another. | Numericals | 2 | never | Never asked | |
| 23 | Average and instantaneous rate from a concentration-time graphSketch [R] and [P] against time, show average rate as the slope of a chord between two times and instantaneous rate as the slope of the tangent at one time, and calculate a value from given readings with units. | Graph | 2 | never | Never asked | |
| 24 | Give reasons: factors affecting rate of reactionFor each factor (surface area, nature of reactants, concentration, temperature, catalyst, radiation) state its effect on rate with a one-line reason and an example. | Give reason | 2 | never | Never asked | |
| 25 | Law of mass action: statement, active mass, exampleState the law of mass action, say that active mass means molar concentration in mol L-1, and write the rate expression it gives for a general reaction aA + bB -> products. | Statement | 1 | never | Never asked | |
| 26 | Zero order: rate equation, unit of k, half-life, graphWrite the integrated rate equation for a zero order reaction, the unit of k, the half-life expression, sketch [A] against t (straight line with slope -k), and give an example. | Statement | 1 | never | Never asked | |
| 27 | Zero order: k, time or concentration leftUse [A] = [A]0 - kt to find k, the time to reach a given concentration, or the concentration left, and t1/2 = [A]0/2k, with units. | Numericals | 2 | never | Never asked | |
| 28 | Derive the integrated rate equation for first orderStart from -d[A]/dt = k[A], separate variables, integrate between [A]0 at t = 0 and [A] at t, and reach k = (2.303/t) log([A]0/[A]). | Derivation | 2 | never | Never asked | |
| 29 | Derive half-life of a first order reactionDefine half-life, put [A] = [A]0/2 at t = t1/2 in the first order equation and show t1/2 = 0.693/k, then state it is independent of initial concentration. | Derivation | 1 | never | Never asked | |
| 30 | Plots for zero and first order; order from plot shapeSketch log[A] against t (straight line, slope -k/2.303) and log([A]0/[A]) against t (slope k/2.303) for first order and [A] against t for zero order, and say which order a given straight-line plot shows. | Graph | 1 | never | Never asked | |
| 31 | Energy profile diagrams: exothermic, endothermic, with catalystDraw potential energy against reaction coordinate for an exothermic and an endothermic reaction, label reactants, products, activated complex, threshold energy, Ea and delta H, and add the lower catalysed path. | Graph | 2 | never | Never asked | |
| 32 | Collision theory: conditions for effective collisionsState the conditions for reaction (particles must collide, with energy at least equal to the threshold energy, and with proper orientation) and use them to explain why only a fraction of collisions give products. | Give reason | 2 | never | Never asked | |
| 33 | Rate law from a mechanism and its slowest stepDefine elementary and complex reactions and rate-determining step, then for a given multi-step mechanism write the rate law from the slow step, the order and the unit of k, and note any intermediate. | Give reason | 2 | never | Never asked | |
| 34 | Why rate rises sharply with temperatureExplain that a rise in temperature increases collisions and, much more, the fraction of molecules with energy at least Ea, so the rate roughly doubles for a 10 degree rise. | Give reason | 1 | never | Never asked |
This list was made from the 2027 syllabus and checked with 9 board papers, including the 2027 specimen paper. It is not yet checked with the textbook.
The 10 topics Chemistry papers ask most
Counted on the board papers from 2018 to the 2027 specimen paper, which every unit has been checked against.
- 1.IUPAC names of coordination compounds from formulaC5 Coordination Compounds · asked 8 times since 2018
- 2.Faraday's first law: mass, charge, current or timeC2 Electrochemistry · asked 7 times since 2018
- 3.Give reasons: transition metal ions are coloured, some colourlessC4 d- and f-Block Elements · asked 7 times since 2018
- 4.Alcohols from Grignard reagent: 1, 2, 3 degreeC7 Alcohols, Phenols and Ethers · asked 7 times since 2018
- 5.Williamson's synthesis of ethersC7 Alcohols, Phenols and Ethers · asked 7 times since 2018
- 6.Identify A, B, C, D in a given reagent chainC8 Aldehydes, Ketones and Carboxylic Acids · asked 7 times since 2018
- 7.Identify compounds from formula and test results (case problem)C8 Aldehydes, Ketones and Carboxylic Acids · asked 7 times since 2018
- 8.Identify A, B, C: amide, Hoffmann and amine-test chainsC9 Organic Compounds containing Nitrogen · asked 7 times since 2018
- 9.Gibbs energy and maximum work from cell emfC2 Electrochemistry · asked 6 times since 2018
- 10.Coordination number and oxidation state of the central metalC5 Coordination Compounds · asked 6 times since 2018