Enthalpy of Reaction

Enthalpy of Reaction MDCAT MCQs with answers

13 past paper MCQs on Enthalpy of Reaction, from the Thermochemistry and Energetics of Chemical Reactions unit of MDCAT Chemistry. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

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1.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.

2.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.

3.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.

4.One slice of bread with a tablespoon of peanut butter on it contains 20g carbohydrate, 10g protein, and 9g fat. Calculate total energy consumed in this intake. (KMU MDCAT 2024)

  1. 158kcal
  2. 173kcal
  3. 201kcal
  4. 218kcal
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Correct answer: (c) 201kcal

Carbohydrate and protein give $4\,\mathrm{kcal}$ a gram and fat $9$, so $80+40+81$ is $201\,\mathrm{kcal}$.

5.Identify standard enthalpy of formation for the following reaction: (NUMS MDCAT 2024)

  1. H2(g) + 1/2 O2(g) → H2O(l)
  2. CO(g) + 1/2 O2(g) → CO2(g)
  3. 2Al(s) + Fe2O3(s) → Al2O3(s) + 2Fe(s)
  4. S(s) + 3/2 O2(g) → SO3(g)
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Correct answer: (a) H2(g) + 1/2 O2(g) → H2O(l)

Only the first makes one mole of a compound from its elements in their standard states.

6.The thermal energy at constan pressure is called: (SZABMU MDCAT 2023)

  1. Enthalpy
  2. Internal energy
  3. Heat capacity
  4. Work done
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Correct answer: (a) Enthalpy

Heat exchanged at constant pressure is the enthalpy change.

7.The correct value for the enthalpy of formation of CO is: (PMC MDCAT 2022)

  1. -110kJ/mol
  2. -210kJ/mol
  3. +110kJ/mol
  4. +210kJ/mol
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Correct answer: (a) -110kJ/mol

Carbon monoxide is formed from its elements with the release of about $110\,\mathrm{kJ\,mol^{-1}}$.

8.Formation of carbon dioxide hinders in calculating the heat of formation of: (PMC Practice 2021)

  1. CCl4
  2. O3
  3. CO
  4. C
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Correct answer: (c) CO

Burning carbon always gives some dioxide as well, so the formation of the monoxide cannot be measured directly.

9.Which of these have a positive value of enthalpy? (PMC Practice 2021)

  1. Combustion
  2. Neutralization
  3. Atomization
  4. All of these options are correct
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Correct answer: (c) Atomization

Atomizing a substance means breaking every bond in it, which always takes energy.

10.Which of the following is always an exothermic process? (PMC Practice 2021)

  1. Enthalpy of atomization
  2. Enthalpy of fusion
  3. Enthalpy of neutralization
  4. Enthalpy of sublimation
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Correct answer: (c) Enthalpy of neutralization

Neutralization of an acid by an alkali always gives out heat.

11.The thermal energy at constant pressure is called: (PMC MDCAT 2020)

  1. Enthalpy
  2. Internal Energy
  3. Heat capacity
  4. Work done
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Correct answer: (a) Enthalpy

Heat exchanged at constant pressure is the enthalpy change.

12.Which of the equations shows ‘’twice’’ the enthalpy change of neutralization as the following equation (UHS MDCAT 2019)

  1. MgCO3 + 2HCl -&gt; MgCl2 + CO2 + H2O
  2. KOH + HCl -&gt; KCl + H2P
  3. NH4Cl + NaOH -&gt; NaCl + H2O + NH3
  4. H2SO4 + Mg(OH)2 -&gt; MgSO4 + 2H2O
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Correct answer: (d) H2SO4 + Mg(OH)2 -&gt; MgSO4 + 2H2O

A diprotic acid with a dibasic alkali makes two moles of water, so twice the heat is given out.

13.Which one of the following enthalpy changes is always exothermic? (UHS MDCAT 2018)

  1. Enthalpy of combustion
  2. Enthalpy of formation
  3. Enthalpy of atomization
  4. Enthalpy of solution
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Correct answer: (a) Enthalpy of combustion

Burning always gives out heat.

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