A gas expands by 2.0 dm³ against a constant external pressure of 1.0 atm. What work is done on the gas (1 dm³ atm = 101.3 J)?
Correct answer D. −203 J
Topic / 40 questions
Thermochemistry and Energetics MCQs
Thermochemistry and Energetics MCQs are multiple-choice questions on the heat changes of chemical reactions, covering enthalpy, internal energy, the first law of thermodynamics, Hess's law and standard enthalpies. They follow the MDCAT chemistry curriculum, and every question on MCQs360 shows its correct answer instantly so you can test both definitions and calculations.
- Gases 40
- Liquids 40
- Solids 40
- Chemical Equilibrium 40
- Reaction Kinetics 40
- Thermochemistry and Energetics 40
- Electrochemistry 40
- Fundamental Concepts of Chemistry 40
- Atomic Structure 39
- Chemical Bonding 39
- Alcohols and Phenols 38
- Industrial Chemistry 37
- Aldehydes and Ketones 37
- Alkyl Halides 37
- s- and p-Block Elements 37
- Chemistry of Hydrocarbons 36
- Fundamental Principles of Organic Chemistry 36
- Carboxylic Acids 36
- Transition Elements 35
- Macromolecules 35
A simple coffee-cup (glass) calorimeter open to the atmosphere directly measures which quantity?
Correct answer A. ΔH, since the reaction occurs at constant pressure
Which conditions are used for standard enthalpy changes in thermochemistry?
Correct answer A. 298 K and 1 atm (101.325 kPa)
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The enthalpy of solution of a substance is the enthalpy change when ____
Correct answer D. one mole of it dissolves in enough solvent to give an infinitely dilute solution
The enthalpy of atomisation of an element is the enthalpy change when ____
Correct answer B. one mole of gaseous atoms is formed from the element in its standard state
What is the approximate enthalpy of neutralisation of a strong acid by a strong base in dilute solution?
Correct answer D. −57.3 kJ mol⁻¹
Given ΔHc of C(s) = −393.5, H₂(g) = −285.8 and CH₄(g) = −890.3 kJ mol⁻¹, what is the standard enthalpy of formation of methane?
Correct answer D. −74.8 kJ mol⁻¹
For N₂(g) + 3H₂(g) → 2NH₃(g) at 298 K, ΔU = −87.4 kJ. What is ΔH (R = 8.314 J K⁻¹ mol⁻¹)?
Correct answer D. −92.4 kJ
A system releases 50 J of heat while 30 J of work is done on it. What is the change in its internal energy?
Correct answer C. −20 J
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Neutralising 0.050 mol of HCl with excess NaOH releases 2.85 kJ of heat. What is the enthalpy of neutralisation?
Correct answer D. −57 kJ mol⁻¹
For an endothermic reaction, how does the enthalpy of the products compare with that of the reactants?
Correct answer D. It is greater
When ammonium chloride dissolves in water, the beaker feels cold. What does this show?
Correct answer C. The dissolution is endothermic
A beaker of hot water left open to the air can exchange both heat and water vapour with its surroundings. It is an example of ____
Correct answer C. an open system
Which pair of quantities are both path functions rather than state functions?
Correct answer D. Heat and work
The specific heat capacity of water is 4.18 J g⁻¹ K⁻¹. What is its molar heat capacity (H₂O = 18 g mol⁻¹)?
Correct answer A. 75.2 J mol⁻¹ K⁻¹
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Which compound is expected to have the most exothermic lattice energy?
Correct answer B. MgO
Which statement about the energy of bond breaking and bond making is correct?
Correct answer D. Breaking bonds absorbs energy and forming bonds releases energy
For which reaction is ΔH equal to ΔU at constant temperature?
Correct answer A. H₂(g) + Cl₂(g) → 2HCl(g)
A reaction has an activation energy of 120 kJ mol⁻¹ in the forward direction and 160 kJ mol⁻¹ in the reverse direction. What is ΔH for the forward reaction?
Correct answer D. −40 kJ mol⁻¹
Which equation represents the standard enthalpy of formation of liquid water?
Correct answer D. H₂(g) + ½O₂(g) → H₂O(l)
About Thermochemistry and Energetics MCQs
The opening questions check key vocabulary: exothermic and endothermic reactions, system and surroundings, open, closed and isolated systems, state functions, heat capacity, internal energy and enthalpy. You will also apply the first law of thermodynamics to find the change in internal energy and compare ΔH with ΔU, including the heat measured in a bomb calorimeter. Further questions test definitions of standard enthalpies of formation, combustion and neutralisation, the use of Hess's law and energy cycles, bond energy calculations and the Born–Haber cycle for lattice energy. Some combine energy profiles with activation energies to find the enthalpy change of a reaction.
Key facts to remember
- First law of thermodynamics: ΔU = q + w, where q is heat absorbed by the system and w is work done on the system.
- At constant pressure the heat change equals ΔH; at constant volume, as in a bomb calorimeter, it equals ΔU.
- ΔH = ΔU + ΔnRT, so ΔH equals ΔU when there is no change in the number of moles of gas.
- Hess's law: the total enthalpy change of a reaction is the same whichever route is taken from reactants to products.
- The standard enthalpy of formation of an element in its standard state, such as O₂(g), is zero.
- Lattice energy cannot be measured directly and is usually found from a Born–Haber cycle.
Exams that include Thermochemistry and Energetics MCQs
Pakistan
- MDCAT
- ECAT
- NUMS
- AKU
- FSc boards
India
- NEET
- JEE Main
Bangladesh
- HSC
- Medical Admission Test
How to prepare for Thermochemistry and Energetics MCQs
- Write out the exact definitions of standard enthalpies of formation, combustion and neutralisation, including the one-mole condition.
- Use a consistent sign convention for q and w in first law questions.
- Draw a small energy cycle for every Hess's law problem rather than adding equations in your head.
- Remember that ΔH = Ea(forward) − Ea(reverse) for energy profile questions.
Frequently asked questions
What does the MDCAT syllabus include in Thermochemistry?
The PMDC MDCAT curriculum covers exothermic and endothermic reactions, system and surroundings, state functions, heat capacity, internal energy and enthalpy, the first law of thermodynamics, Hess's law and energy cycles, and enthalpy of reaction.
Which exams ask Thermochemistry MCQs?
Thermochemistry appears in MDCAT, ECAT, NUMS and AKU entry tests and in FSc board papers in Pakistan. In India it is part of chemical thermodynamics in NEET and JEE Main, and in Bangladesh it is tested in HSC and medical admission tests.
Why is the enthalpy of neutralisation of a weak acid less negative?
A weak acid such as ethanoic acid is only partly ionised in water. Some of the energy released during neutralisation is used to ionise the remaining acid molecules, so the overall enthalpy change is less negative than the value for a strong acid and strong base.
Last reviewed October 2026