Free Thermochemistry and Energetics of Chemical Reactions MCQs with Answers
728 Thermochemistry and Energetics of Chemical Reactions MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Thermochemistry measures energy changes in chemical reactions and distinguishes exothermic from endothermic processes. Work covers systems, surroundings and state functions, internal energy, the first law of thermodynamics, enthalpy and Hess's law, including the sign conventions used when heat enters or leaves a system.
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728 questions · page 34 of 37
- A. A: Remains constant
- B. B: Decreases
- C. C: Increases
- D. D: Remains unchanged
Explanation: Option B is correct because in an endothermic reaction, heat is absorbed from the surroundings, resulting in a decrease in the temperature…
Correct answer: B: Decreases- A. Release of energy
- B. Absorption of energy
- C. No change in energy
- D. Sharing of nucleus
Explanation: During bond formation, energy is released as atoms achieve a more stable, lower-energy state.
Correct answer: Release of energy- A. 15 kJ/mol
- B. -17 kJ/mol
- C. 16.2 kJ/mol
- D. -16.5 kJ/mol
Explanation: The enthalpy of solution (∆Hosol) of ammonium chloride (NH4Cl) is +16.2 kJ/mol.
Correct answer: 16.2 kJ/mol- A. Translational energy only
- B. All kinds of kinetic energy
- C. Elastic potential energy only
- D. All of these
Explanation: Internal energy is the total of all types of energy present within a system.
Correct answer: All of these- A. Fusion
- B. Vaporization
- C. Sublimation
Explanation: Sublimation is a phase transition in which a substance changes directly from a solid to a gas without passing through the liquid phase.
Correct answer: Sublimation- A. Exothermic reactions
- B. Decomposition reactions
- C. Dissociation reactions
- D. Endothermic reactions
Explanation: In exothermic reactions, the system releases heat to the surroundings, causing the enthalpy change (∆H) to be negative.
Correct answer: Exothermic reactions- A. -676 kJ mol-1
- B. -110 kJ mol-1
- C. 110 kJ mol-1
- D. 676 kJ mol-1
Explanation: To find the enthalpy change for the combustion of graphite to form CO, apply Hess's Law by using the given reactions.
Correct answer: -110 kJ mol-1- A. Vibrational energy
- B. Rotational energy
- C. Translational energy
- D. Rnergy due to gravitation
Explanation: The correct answer is gravitational energy.Internal energy is the total energy of a system, including the kinetic energy and potential…
Correct answer: Rnergy due to gravitation- A. ∆H = 0
- B. ∆H > ∆E
- C. ∆H = ∆E
- D. ∆H < ∆E
Explanation: For the reaction 2 NH3 ➞ N2 + 3 H2, the correct statement is that ∆H = ∆E.
Correct answer: ∆H = ∆E- A. It is an endothermic process
- B. Formation of water is a spontaneous process
- C. It is the heat evolved for complete reaction of 2 moles of oxygen with excess of hydrogen
- D. Water is at lower energy than its reactants
Explanation: The correct answer is that water is at lower energy than its reactants.
Correct answer: Water is at lower energy than its reactants- A. H2 + I2 ➞ 2HI
- B. 2H2O2 ➞ 2H2O + O2
- C. PCl5 ➞ PCl3 + Cl2
- D. C + O2 ➞ CO2
Explanation: The correct answer is H2 + I2 ➞ 2HI. In this reaction, the change in the number of moles of gas (∆n) is zero, so the change in enthalpy…
Correct answer: H2 + I2 ➞ 2HI- A. The change in heat content
- B. The total energy change at constant pressure
- C. The heat change at constant volume if ∆n=0
- D. Work done at constant pressure
Explanation: Enthalpy change, represented by ΔH, is the total energy change in a system at constant pressure.
Correct answer: The total energy change at constant pressure- A. Joule
- B. Kelvin
- C. Calorie
- D. Kilojoule (kJ)
Explanation: Option B is correct because Kelvin is the unit for measuring temperature, not heat.
Correct answer: Kelvin- A. Universe
- B. Boundary
- C. System
- D. Surroundings
Explanation: The correct answer is Option C: System. In thermochemistry, a system is the specific portion of the universe that is being studied…
Correct answer: System- A. HCl(g) ➞ H(g) + Cl(g)
- B. HCl(g) ➞ 1/2 H2(g) + 1/2 Cl2(g)
- C. 2HCl(g) ➞ H2(g) + Cl2(g)
- D. HCl(g) ➞ H(g) + Cl-(g)
Explanation: The correct answer is Option A:HCl(g) ➞ H(g) + Cl(g). This reaction represents the breaking of the H-Cl bond to form individual hydrogen…
Correct answer: HCl(g) ➞ H(g) + Cl(g)- A. oiling point
- B. Molarity
- C. Freezing point
- D. All
Explanation: An extensive property of a system is that property which depends upon the amount of the substance or substances e.g.
Correct answer: All- A. Tf > Ti for reversible process but Tf = Ti for irreversible process.
- B. (Tf)reversible = (Tf)irreversible
- C. Tf = Ti for both reversible and irreversible processes
- D. (Tf)irreversible > (Tf)reversible
Explanation: During the irreversible expansion of an ideal gas in an isolated system (free expansion), the temperature decreases.
Correct answer: (Tf)irreversible > (Tf)reversible- A. H+ (aq) + OH-(aq) -> H2O(l)
- B. H2 (g) + ½ O2 (g) -> H2O (l)
- C. H2O(g) + H2O(l)
- D. H2O(s) -> H2O(l)
Explanation: The reaction H₂(g) +1/2 O₂(g) → H₂O(l) shows the standard enthalpy change for the formation of water, where △H is the heat of formation of…
Correct answer: H2 (g) + ½ O2 (g) -> H2O (l)- A. Enthalpy of atomization
- B. Enthalpy of fusion
- C. Enthalpy of vaporization
- D. Enthalpy of formation
Explanation: Option A, enthalpy of atomization, is the energy required to completely separate all the atoms in a chemical substance.
Correct answer: Enthalpy of atomization- A. Heat of fusion
- B. Heat of vapourization
- C. Heat of sublimation
- D. Heat of evaporation
Explanation: The heat of fusion is the enthalpy change required to melt one mole of a solid substance at its melting point The heat of vaporization is…
Correct answer: Heat of sublimation