Thermochemistry and Energetics of Chemical Reactions

Thermochemistry and Energetics of Chemical Reactions MDCAT MCQs with answers

50 past paper MCQs from Chemistry unit 8, Thermochemistry and Energetics of Chemical Reactions, across 7 topics. They are arranged topic by topic; bigger topics show a sample here and link to their full set and to study notes. Tap “Show answer” for the correct option and a short solution.

Practise as a quiz

Exothermic and Endothermic Reactions

1.In an exothermic reaction, the heat content of the: (MDCAT 2024)

  1. reactants and products is equal
  2. reactants is more than that of the products
  3. products is more than that of the reactants
  4. reactants and products does not change
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Correct answer: (b) reactants is more than that of the products

Heat is given out, so the products hold less energy than the reactants and $\Delta H$ is negative.

2.Majority of reactions taking place at ordinary temperatures with -ΔH are (UHS MDCAT 2025)

  1. Endothermic
  2. Exothermic
  3. Thermally unstable
  4. Reversible
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Correct answer: (b) Exothermic

A negative enthalpy change means heat leaves the system, which is what exothermic means.

3.Select the exothermic reaction among the following: (NUMS MDCAT 2025)

  1. Thermal composition of P2O5
  2. Formation of atmospheric nitric oxide
  3. Burning of methane
  4. Sublimation of dry ice
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Correct answer: (c) Burning of methane

Burning methane gives out heat, so its enthalpy change is negative.

All 8 Exothermic and Endothermic Reactions MCQs → Exothermic and Endothermic Reactions notes →

Thermodynamics

4.Select the spontaneous reaction from the following: (NUMS MDCAT 2025)

  1. Reaction of nitrogen and oxygen
  2. Emission of α-particles from polonium
  3. Thermal decomposition of marble
  4. Burning of paper
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Correct answer: (b) Emission of α-particles from polonium

Alpha emission needs no help from outside; the other three must be driven or lit.

Terms Used in Thermochemistry

5.Which of the following terms is a state function? (MDCAT 2022)

  1. freezing
  2. decomposition
  3. sublimation
  4. enthalpy
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Correct answer: (d) enthalpy

Enthalpy depends only on the state of the system, not on the path by which it got there.

6.Which of the following is NOT a state function? (SIBA MDCAT 2025)

  1. Enthalpy
  2. Work
  3. Internal energy
  4. Pressure
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Correct answer: (b) Work

Work depends on the path taken, so it is not fixed by the state of the system.

7.Q.89 Which of the following term is state function? (UHS MDCAT 2023)

  1. freezing
  2. decomposition
  3. sublimation
  4. enthalpy
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Correct answer: (d) enthalpy

Enthalpy depends only on the state of the system, not on how it got there.

All 10 Terms Used in Thermochemistry MCQs → Terms Used in Thermochemistry notes →

Hess's Law

8.The Born-Haber cycle is used to determine the lattice energy of ionic compounds. It is an application of: (MDCAT 2022)

  1. Henry's law
  2. Le Chatelier's principle
  3. Hess's law
  4. the common ion effect
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Correct answer: (c) Hess's law

The cycle adds the enthalpies of a set of steps to reach the same final state, which is Hess's law.

9.The heat of formation of CO and CO2 are -26.4 Kcal and -94.0 Kcal respectively. The heat of combustion of carbon monoxide according to Hess's Law will be: (SIBA MDCAT 2025)

  1. +26.4Kcal
  2. -67.6Kcal
  3. +94.0Kcal
  4. -120.4Kcal
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Correct answer: (b) -67.6Kcal

Burning carbon monoxide is the formation of carbon dioxide less the formation of the monoxide, $-94.0-(-26.4)$, or $-67.6\,\mathrm{kcal}$.

10.ΔH can be measured indirectly by applying (KMU MDCAT 2024)

  1. Avogadro's law
  2. Faraday's law
  3. Gas's law
  4. Hess's law
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Correct answer: (d) Hess's law

Hess’s law lets an enthalpy change be got from any convenient route between the same two states.

All 7 Hess's Law MCQs → Hess's Law notes →

Enthalpy of Reaction

11.The enthalpy change when one mole of water is formed by the reaction of an acid with an alkali under standard conditions is known as the: (MDCAT 2024)

  1. enthalpy of formation
  2. enthalpy of reaction
  3. enthalpy of combustion
  4. enthalpy of neutralization
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Correct answer: (d) enthalpy of neutralization

Acid plus alkali making one mole of water is the enthalpy of neutralization.

12.For endothermic reaction, enthalpy change is: (SZABMU MDCAT 2025)

  1. ΔHreactant>ΔHproduct
  2. ΔHreactant<ΔHproduct
  3. ΔHreactant=ΔHproduct
  4. ΔHreactant=ΔHproduct=0
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Correct answer: (b) ΔHreactant<ΔHproduct

An endothermic reaction takes heat in, so the products hold more enthalpy than the reactants.

13.The enthalpy change when1 Mole of water is formed by the reaction of acid with an alkali under standard conditions is known as: (UHS MDCAT 2024)

  1. Enthalpy of formation
  2. Enthalpy of reaction
  3. Enthalpy of combustion
  4. Enthalpy of neutralization
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Correct answer: (d) Enthalpy of neutralization

That is the enthalpy of neutralization.

All 13 Enthalpy of Reaction MCQs → Enthalpy of Reaction notes →

Internal Energy

14.If 100 KJ of heat is absorbed by the system and 40 KJ of work is done on the system what is the change of Internal energy? (UHS MDCAT 2025)

  1. -60 KJ
  2. +60 KJ
  3. -140 KJ
  4. +140 KJ
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Correct answer: (d) +140 KJ

Heat absorbed and work done on the system both add, so the internal energy rises by $140\,\mathrm{kJ}$.

15.An increase in the internal energy of a chemical system can lead to all EXCEPT: (KMU MDCAT 2025)

  1. An increase in temperature due to rise in kinetic energy of molecules
  2. A phase change such as melting or evaporation
  3. A chemical reaction if energy supplied is sufficient to break bonds
  4. An increase in temperature due to drop in kinetic energy of molecules
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Correct answer: (d) An increase in temperature due to drop in kinetic energy of molecules

Internal energy rises with the kinetic energy of the molecules, so a drop in that energy cannot raise the temperature.

16.When 1 mole of ice melts at 0°C and constant pressure of 1 atmosphere, 6025 J of heat is absorbed by the system. The molar volume of ice and water are 0.020 and 0.018 dm³, respectively. Calculate ΔE. (1dm³.atm=101.33J) (KMU MDCAT 2024)

  1. 6010.20J
  2. 6015.20J
  3. 6020.20J
  4. 6025.20J
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Correct answer: (d) 6025.20J

The volume falls slightly on melting, so the surroundings do a little work and $\Delta E$ is a shade above the heat absorbed.

Internal Energy notes →

Laws of Thermodynamics

17.Calculate the work done when 1 mole of an ideal gas expands from 15 dm³ to 20 dm³ against a constant external pressure of 2 atmospheres. (KMU MDCAT 2024)

  1. -10 atm.dm³
  2. -5 atm.dm³
  3. 5 atm.dm³
  4. 10 atm.dm³
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Correct answer: (a) -10 atm.dm³

$w=-P\Delta V=-2\times5$, which is $-10\,\mathrm{atm\,dm^3}$; the sign says the gas did the work.

18.Expansion takes place when gas evolves during reaction between carbohydrates and dilute HCl. Predict energy change and work done: (NUMS MDCAT 2024)

  1. w is positive, q is negative
  2. w is negative, q is positive
  3. q is positive, no work done
  4. w is positive, q is positive
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Correct answer: (b) w is negative, q is positive

The gas pushes back the surroundings, so the system does work and the sign of $w$ is negative while heat is absorbed.

19.The correct equation for the first law of thermodynamics is: (SZABMU MDCAT 2023)

  1. ∆E = q + w
  2. ∆E = w - q
  3. ∆E = ∆q - p∆v
  4. ∆E = ∆q + p∆v
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Correct answer: (a) ∆E = q + w

The first law is $\Delta E=q+w$: heat put in and work done on the system.

All 8 Laws of Thermodynamics MCQs → Laws of Thermodynamics notes →

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