JEE Main · Chemistry · Thermodynamics (Chemistry)
Enthalpy and Hess's Law: JEE Main previous year questions
62 questions in the 108 JEE Main shifts Lumi analysed, in 8 of 8 years. Pattern: Asked most years. 20 came in 2024–26. Here is how it is asked and which ideas come back.
- Questions
- 62
- in 57 of 108 shifts
- Years asked
- 8/8
- last asked 2026
- Weighted estimate
- 0.6
- model; history: 0.6 a shift on average, typically 0.4–0.8
Key findings
- 01
Asked in 8 of 8 years with analysed shifts and in 57 of 108 shifts: 62 questions, #36 of 196 topics. It came in every year with analysed shifts.
- 02
41% of its questions since 2020 tested an idea no earlier year had asked; 23 repeated an idea from the year before.
- 03
The most repeated idea is Relation Between ΔH and ΔU, asked 10 times in 10 shifts (2020, 2021, 2022, 2024), most often as “identify incorrect thermodynamic relation”.
- 04
JEE Main has asked 23 of the 48 ideas in this topic; 16 have never been asked, directly or inside another question.
- 05
Mostly asked as numerical value (74%); 74% need a numerical answer, 44% are easy and 5% hard.
- 06
The skill tested most is calculation (69%), then conceptual (18%).
Questions a shift, year by year
Out of the 25 Chemistry questions in a shift. Years differ in how many shifts Lumi analysed, so each year is scaled to one shift.
Raw count: 2017: 1 in 1 shift · 2020: 4 in 12 shifts · 2021: 12 in 24 shifts · 2022: 17 in 24 shifts · 2023: 8 in 12 shifts · 2024: 8 in 18 shifts · 2025: 8 in 8 shifts · 2026: 4 in 9 shifts.
- Up to 2023
- 0.6
- a shift, of 25
- Since 2024
- 0.6
- 0.0
- Usual gap
- 1.3 yrs
- between years asking it
- Shifts with it
- 57/108
- 53% of analysed shifts
Recent framings
- numerical: enthalpy of reaction from formation enthalpies
- numerical: enthalpy of formation from bomb calorimetry
- statement I/II on heat capacities of ideal gas
Revise first
- Bomb Calorimetry Calculations · asked 2021, 2022, 2023, 2024, 2025, 2026
- Hess's Law · asked 2017, 2021, 2022, 2024, 2026
- Formation and Combustion · asked 2021, 2022, 2023, 2024, 2026
How it is asked
Difficulty, format and skill
Across all 62 questions on Enthalpy and Hess's Law since 2017.
Difficulty
QUESTIONS- Easy27 · 44%
- Medium32 · 52%
- Hard3 · 5%
Format
SHARE- Numerical value · 46 Q74%
- Single correct · 12 Q19%
- Two statements · 2 Q3%
- Assertion–reason · 1 Q2%
- Other · 1 Q2%
Skill tested
SHARE- Calculation · 43 Q69%
- Conceptual · 11 Q18%
- Multi-step · 7 Q11%
- Recall · 1 Q2%
Repeats
New idea, or one asked before?
Each column is a year. Blue questions tested an idea no earlier year had asked; navy ones went back to an idea from an earlier year. 2017 is the first year, so everything in it counts as new. Heights are question counts, and Lumi analysed 1 to 24 shifts a year, so compare the split inside a column rather than heights across years.
- Idea asked for the first time
- Idea asked in an earlier year
Coverage of the topic
JEE Main has asked 23 of the 48 ideas in this topic. 16 have never been asked yet.
- Asked directly23 · 48%
- Touched inside another question9 · 19%
- Never asked16 · 33%
Ideas come from Lumi’s JEE syllabus map. A never-asked idea is not a safe skip: across all of JEE Main, 22% of questions since 2024 tested an idea no earlier year had asked.
Drill down
Chapter, idea, question
Every idea JEE Main tested in this topic, with its eight years. Open one to read the questions.
22 ideas inside
Squares are the 8 years with analysed shifts, 2017 to 2026. A number is the questions that year when there is more than one; the shade is scaled to one shift, so a year with more analysed shifts (1 to 24 a year) does not look darker. Share is of the level above.
Ideas
Every idea inside this topic
23 different ideas were tested; 12 came more than once.
identify incorrect thermodynamic relation
Numerical value · 10 shifts · 9 numericalenthalpy of formation from bomb calorimetry
Numerical value · 7 shifts · 7 numericalenthalpy of reaction from formation enthalpies
Numerical value · 7 shifts · 4 numericalenthalpy of formation via hess cycle
Numerical value · 5 shifts · 3 numericalenthalpy of formation from bond enthalpies
Numerical value · 5 shifts · 5 numericalstatement i/ii on heat capacities of ideal gas
Numerical value · 3 shifts · 1 numericalstatement i/ii on melting of ice
Numerical value · 3 shifts · 1 numericalassertion reason enthalpy of neutralisation
Numerical value · 3 shifts · 2 numericalheat of solution from lattice and hydration energies
Numerical value · 2 shifts · 1 numericalcount endothermic processes
Numerical value · 2 shifts · 2 numericalheat evolved per gram of mixture
Numerical value · 2 shifts · 2 numericallattice enthalpy via born-haber cycle
Numerical value · 2 shifts · 2 numericaltrue statement selection on enthalpy of solution
Single correct · 1 shiftresonance energy from bond energies
Numerical value · 1 shift · 1 numericaltrue statement selection on standard state
Single correct · 1 shiftheat ratio of neutralisation
Numerical value · 1 shift · 1 numericalheat capacity from electrical heating at constant volume
Numerical value · 1 shift · 1 numericalcount intensive properties among given
Numerical value · 1 shift · 1 numericalenthalpy of formation via hess cycle
Single correct · 1 shiftcount state functions
Numerical value · 1 shift · 1 numericalenthalpy of ionization of acetic acid
Numerical value · 1 shift · 1 numericalenthalpy of sublimation from fusion and vaporisation
Numerical value · 1 shift · 1 numericalrelation between atomisation enthalpy and bond enthalpy
Single correct · 1 shift
| Idea | Years asked | Times | Shifts | Format | Numerical |
|---|---|---|---|---|---|
| Relation Between ΔH and ΔUidentify incorrect thermodynamic relation | 10 | 10 | Numerical valueCalculation | 9 | |
| Bomb Calorimetry Calculationsenthalpy of formation from bomb calorimetry | 7 | 7 | Numerical valueCalculation | 7 | |
| Formation and Combustionenthalpy of reaction from formation enthalpies | 7 | 7 | Numerical valueCalculation | 4 | |
| Hess's Lawenthalpy of formation via hess cycle | 5 | 5 | Numerical valueCalculation | 3 | |
| Bond Enthalpy Calculationsenthalpy of formation from bond enthalpies | 5 | 5 | Numerical valueCalculation | 5 | |
| Heat Capacity Relation in Enthalpystatement i/ii on heat capacities of ideal gas | 3 | 3 | Numerical valueConceptual | 1 | |
| Enthalpy of Phase Transitionsstatement i/ii on melting of ice | 3 | 3 | Numerical valueCalculation | 1 | |
| Constant Enthalpy of Neutralizationassertion reason enthalpy of neutralisation | 3 | 3 | Numerical valueCalculation | 2 | |
| Enthalpy of Solution and Hydrationheat of solution from lattice and hydration energies | 2 | 2 | Numerical valueCalculation | 1 | |
| Sign Conventions for Heat Flowcount endothermic processes | 2 | 2 | Numerical valueCalculation | 2 | |
| Standard Enthalpy of Reactionheat evolved per gram of mixture | 2 | 2 | Numerical valueCalculation | 2 | |
| Born-Haber Cycle for Lattice Enthalpylattice enthalpy via born-haber cycle | 2 | 2 | Numerical valueCalculation | 2 | |
| Enthalpy of Dilutiontrue statement selection on enthalpy of solution | 1 | 1 | Single correctConceptual | – | |
| Resonance Energy Calculationresonance energy from bond energies | 1 | 1 | Numerical valueMulti-step | 1 | |
| Standard Reference States of Elementstrue statement selection on standard state | 1 | 1 | Single correctConceptual | – | |
| Neutralization Enthalpy of Polybasic Acidsheat ratio of neutralisation | 1 | 1 | Numerical valueCalculation | 1 | |
| Enthalpy and Heat Capacityheat capacity from electrical heating at constant volume | 1 | 1 | Numerical valueCalculation | 1 | |
| Extensive Nature of Enthalpycount intensive properties among given | 1 | 1 | Numerical valueConceptual | 1 | |
| Manipulating Thermochemical Equationsenthalpy of formation via hess cycle | 1 | 1 | Single correctCalculation | – | |
| Enthalpy as a State Functioncount state functions | 1 | 1 | Numerical valueConceptual | 1 | |
| Enthalpy of Ionization of Weak Acids/Basesenthalpy of ionization of acetic acid | 1 | 1 | Numerical valueCalculation | 1 | |
| Enthalpies of Phase Transitionsenthalpy of sublimation from fusion and vaporisation | 1 | 1 | Numerical valueCalculation | 1 | |
| Enthalpy of Atomizationrelation between atomisation enthalpy and bond enthalpy | 1 | 1 | Single correctConceptual | – |
Times and shifts count every analysed shift. Across JEE Main, 78% of questions since 2024 went back to an idea an earlier year had asked; the rest were new. All repeated ideas
Every question
Enthalpy and Hess's Law questions, year by year
The newest 40 show their opening words as they appeared in the official paper; older ones name the idea they tested. Open one for its options and the official answer.
JEE Main 20264 questions in 4 shifts
- 2 Apr, Shift 1Q54Consider the following data. (i) kJ/mol (ii)…
Idea: Hess's Law
HardSingle correct - 4 Apr, Shift 1Q54Given below are two statements: Statement I: For an ideal gas, heat capacity at constant volume is always greater than the heat capacity…
Idea: Heat Capacity Relation in Enthalpy
EasyTwo statements - 4 Apr, Shift 2Q71If 3.365 g of ethanol () is burnt completely in a bomb calorimeter at 298.15 K, the heat produced is 99.472 kJ. The…
Idea: Bomb Calorimetry Calculations
Asked the year beforeHardNumerical value - 8 Apr, Shift 2Q74Consider the reaction The magnitude of enthalpy…
Idea: Formation and Combustion
EasyNumerical value
JEE Main 20258 questions in 6 shifts
- 3 Apr, Shift 1Q71Given : [C (graphite)] = 710 kJ mol = 414 kJ mol…
Idea: Bond Enthalpy Calculations
Asked the year beforeMediumNumerical value - 3 Apr, Shift 2Q53Given below are two statements: Statement I : When a system containing ice in equilibrium with water (liquid) is heated, heat is absorbed…
Idea: Enthalpy of Phase Transitions
EasyTwo statements - 3 Apr, Shift 2Q72A sample of n-octane (1.14 g) was completely burnt in excess of oxygen in a bomb calorimeter, whose heat capacity is 5 kJ…
Idea: Bomb Calorimetry Calculations
Asked the year beforeMediumNumerical value - 4 Apr, Shift 2Q52Consider the given data : (a) kJ mol (b)…
Idea: Enthalpy of Dilution
New ideaMediumSingle correct - 7 Apr, Shift 1Q53Total enthalpy change for freezing of 1 mol of water at C to ice at C is __________ (Given: …
Idea: Enthalpy of Phase Transitions
MediumSingle correct - 7 Apr, Shift 2Q52The correct statement amongst the following is :
Idea: Standard Reference States of Elements
New ideaMediumSingle correct - 7 Apr, Shift 2Q53The hydration energies of and are and kJ/mol respectively. If lattice energy of KCl is …
Idea: Enthalpy of Solution and Hydration
Asked the year beforeEasySingle correct - 8 Apr, Shift 2Q73Resonance in can be represented as…
Idea: Resonance Energy Calculation
New ideaHardNumerical value · figure
JEE Main 20248 questions in 6 shifts
- 4 Apr, Shift 1Q83The enthalpy of formation of ethane () from ethylene by addition of hydrogen where the bond-energies of CH, CC,…
Idea: Bond Enthalpy Calculations
Asked the year beforeEasyNumerical value - 5 Apr, Shift 1Q72Given below are two statements : One is labelled as Assertion (A) and the other is labelled as Reason (R) Assertion (A) : Enthalpy of…
Idea: Constant Enthalpy of Neutralization
EasyAssertion–reason - 5 Apr, Shift 1Q83The heat of combustion of solid benzoic acid at constant volume is kJ at C. The heat of combustion at constant…
Idea: Bomb Calorimetry Calculations
Asked the year beforeMediumNumerical value - 5 Apr, Shift 2Q83Combustion of 1 mole of benzene is expressed at . The…
Idea: Formation and Combustion
Asked the year beforeMediumNumerical value - 8 Apr, Shift 2Q84for water is at 1 bar and 100 °C. Change in internal energy for this…
Idea: Relation Between ΔH and ΔU
EasyNumerical value - 9 Apr, Shift 1Q83The heat of solution of anhydrous and are kJ mol and kJ mol…
Idea: Enthalpy of Solution and Hydration
New ideaEasyNumerical value - 9 Apr, Shift 1Q84When equal volume of 1M HCl and 1M are separately neutralised by excess volume of 1M NaOH solution, and kJ of…
Idea: Neutralization Enthalpy of Polybasic Acids
New ideaEasyNumerical value - 30 Jan, Shift 2Q82Two reactions are given below:…
Idea: Hess's Law
EasyNumerical value
JEE Main 20238 questions in 8 shifts
- 6 Apr, Shift 2Q83Consider the following data Heat of combustion of = kJ mol Heat of combustion of =…
Idea: Formation and Combustion
Asked the year beforeMediumNumerical value - 8 Apr, Shift 1Q84When a 60 W electric heater is immersed in a gas for 100s in a constant volume container with adiabatic walls, the temperature of the gas…
Idea: Enthalpy and Heat Capacity
New ideaEasyNumerical value - 8 Apr, Shift 2Q83For complete combustion of ethene, the amount of heat produced as measured…
Idea: Bomb Calorimetry Calculations
Asked the year beforeMediumNumerical value - 10 Apr, Shift 1Q62Given (A) (B)…
Idea: Manipulating Thermochemical Equations
New ideaEasySingle correct - 10 Apr, Shift 2Q83The number of endothermic process/es from the following is ____________ A. (g) 2I (g) B. HCl (g)…
Idea: Sign Conventions for Heat Flow
EasyNumerical value - 11 Apr, Shift 1Q83Solid fuel used in rocket is a mixture of and Al (in ratio 1:2). The heat evolved (kJ) per gram of the mixture is…
Idea: Standard Enthalpy of Reaction
MediumNumerical value - 11 Apr, Shift 2Q84The total number of intensive properties from the following is ____________ Volume, Molar heat capacity, Molarity, …
Idea: Extensive Nature of Enthalpy
New ideaEasyNumerical value - 13 Apr, Shift 1Q83. AB, and …
Idea: Bond Enthalpy Calculations
MediumNumerical value
JEE Main 202217 questions in 17 shifts
- 25 Jul, Shift 1Q82Asked the year beforeEasyNumerical value
- 25 Jul, Shift 2Q84While performing a thermodynamics experiment, a student made the following observations. …
Idea: Enthalpy of Ionization of Weak Acids/Bases
New ideaMediumNumerical value - 26 Jul, Shift 1Q842.4 g coal is burnt in a bomb calorimeter in excess of oxygen at 298 K and 1 atm pressure. The temperature of the calorimeter rises from…
Idea: Bomb Calorimetry Calculations
Asked the year beforeMediumNumerical value - 26 Jul, Shift 2Q83For the reaction = −59.6 kJ at 27°C. The enthalpy change…
Idea: Relation Between ΔH and ΔU
Asked the year beforeEasyNumerical value - 27 Jul, Shift 1Q84The molar heat capacity for an ideal gas at constant pressure is 20.785 J Kmol. The change in internal energy is 5000 J upon…
Idea: Heat Capacity Relation in Enthalpy
MediumNumerical value - 27 Jul, Shift 2Q83A gas (Molar mass=280 g ) was burnt in excess in a constant volume calorimeter and during combustion the…
Idea: Bomb Calorimetry Calculations
Asked the year beforeMediumNumerical value - 28 Jul, Shift 1Q62Which of the following relation is not correct ?
Idea: Relation Between ΔH and ΔU
Asked the year beforeEasySingle correct - 28 Jul, Shift 2Q60Among the following the number of state variables is ______. Internal energy (U) Volume (V) Heat (q) Enthalpy (H)
Idea: Enthalpy as a State Function
New ideaEasyNumerical value - 29 Jul, Shift 1Q84When 600 mL of 0.2 M is mixed with 400 mL of 0.1 M NaOH solution in a flask, the rise in temperature of the flask is…
Idea: Constant Enthalpy of Neutralization
Asked the year beforeMediumNumerical value - 29 Jul, Shift 2Q63…
Idea: Formation and Combustion
Asked the year beforeMediumSingle correct - 24 Jun, Shift 2Q64At 25°C and 1 atm pressure, the enthalpies of combustion are given below: Substance | H | C (graphite) | CH(g)…
Idea: Formation and Combustion
Asked the year beforeMediumSingle correct - 25 Jun, Shift 2Q62At 25°C and 1 atm pressure, the enthalpy of combustion of benzene (l) and acetylene (g) are -3268 and -1300…
Idea: Formation and Combustion
Asked the year beforeMediumSingle correct - 26 Jun, Shift 1 · Q81Relation Between ΔH and ΔUAsked the year beforeMedium
- 26 Jun, Shift 2 · Q84Relation Between ΔH and ΔUAsked the year beforeMedium
- 28 Jun, Shift 2 · Q82Relation Between ΔH and ΔUAsked the year beforeMedium
- 29 Jun, Shift 1 · Q82Enthalpy of Phase TransitionsNew ideaEasy
- 29 Jun, Shift 2 · Q82Relation Between ΔH and ΔUAsked the year beforeMedium
JEE Main 202112 questions in 11 shifts
- 4 Aug, Shift 2 · Q55Hess's LawMedium
- 26 Aug, Shift 1 · Q53Born-Haber Cycle for Lattice EnthalpyNew ideaMedium
- 26 Aug, Shift 2 · Q53Relation Between ΔH and ΔUAsked the year beforeMedium
- 27 Aug, Shift 1 · Q52Constant Enthalpy of NeutralizationNew ideaMedium
- 25 Feb, Shift 1 · Q53Bomb Calorimetry CalculationsNew ideaMedium
- 25 Feb, Shift 1 · Q57Born-Haber Cycle for Lattice EnthalpyNew ideaEasy
- 26 Feb, Shift 2 · Q54Bond Enthalpy CalculationsNew ideaMedium
- 22 Jul, Shift 2 · Q54Formation and CombustionNew ideaEasy
- 25 Jul, Shift 1 · Q55Enthalpies of Phase TransitionsNew ideaEasy
- 25 Jul, Shift 2 · Q54Sign Conventions for Heat FlowNew ideaEasy
- 17 Mar, Shift 1 · Q54Standard Enthalpy of ReactionNew ideaEasy
- 18 Mar, Shift 1 · Q53Bond Enthalpy CalculationsNew ideaEasy
JEE Main 20204 questions in 4 shifts
- 9 Jan, Shift 1 · Q28Enthalpy of AtomizationNew ideaMedium
- 2 Sep, Shift 1 · Q46Relation Between ΔH and ΔUNew ideaEasy
- 2 Sep, Shift 2 · Q47Relation Between ΔH and ΔUNew ideaMedium
- 4 Sep, Shift 1 · Q29Heat Capacity Relation in EnthalpyNew ideaMedium
JEE Main 20171 question in 1 shift
Questions from the official JEE Main Paper 1 shifts published by NTA (CBSE for 2017). Questions NTA dropped are left out. Topic and idea tags, counts and notes are Lumi’s.