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 5 of 37
- A. Neutralization
- B. Combustion
- C. Atomization
- D. All of these
Explanation: Atomization is the process of breaking all the bonds in a substance to form individual gaseous atoms.
Correct answer: Atomization- A. ∆H = qv + w
- B. ∆H = E + PV
- C. ∆H = qp + PV
- D. ∆H = E
Explanation: In symbols, the enthalpy, H, equals the sum of the internal energy, E, and the product of the pressure, P, and volume, V, of the system: H…
Correct answer: ∆H = E + PV- A. 300 K and 2 atm
- B. 300 K and 1atm
- C. 298 K and 1 atm
- D. 295 K and 1 atm
Explanation: Enthalpy is measured at standard conditions i.e. 298 K and 1 atm.
Correct answer: 298 K and 1 atm- A. Volume
- B. Pressure
- C. Temperature
- D. Mass
Explanation: At a constant pressure, the heat flow for any process is equal to the change in the internal energy of the system plus the work done (PV).
Correct answer: Pressure- A. ∆H is always less than ∆U
- B. ∆H is always greater than ∆U
- C. ∆H is less than ∆U if the number of moles of gaseous products is greater than the number of moles of gaseous reactants.
- D. ∆H is less than ∆U if the number of moles of gaseous products is less than the number of moles of gaseous reactants.
Explanation: The relationship is ΔH = ΔU + ΔngRT. If the number of moles of gas decreases during the reaction, Δng is negative.
Correct answer: ∆H is less than ∆U if the number of moles of gaseous products is less than the number of moles of gaseous reactants.- A. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
- B. 2CH4(g) + 4O2(g) → 2CO2(g) + 4H2O(g)
- C. CH4(s) + 2O2(g) → CO2(g) + 2H2O(g)
- D. CH4(l) + 2O2(g) → CO2(g) + 2H2O(g)
Explanation: The standard enthalpy of combustion is defined for the combustion of one mole of a substance in its standard state.
Correct answer: CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)- A. Enthalpy of formation
- B. Enthalpy of neutralization
- C. Enthalpy of solution
- D. Enthalpy of combustion
Explanation: Enthalpy of formation, enthalpy of neutralization and enthalpy of solution can be determined by glass calorimeter.
Correct answer: Enthalpy of combustion- A. Endothermic
- B. Exothermic
- C. Both a and b
- D. None of these
Explanation: The burning of fuel is an exothermic process. During combustion, the chemical bonds in the fuel molecules break, and new bonds are formed…
Correct answer: Exothermic- A. Enthalpy of atomization
- B. Enthalpy of fusion
- C. Enthalpy of neutralization
- D. Enthalpy of sublimation
Explanation: Option A: Enthalpy of atomization is the heat required to dissociate a compound into its constituent atoms.
Correct answer: Enthalpy of neutralization- A. 58 gm
- B. 56 gm
- C. 54 gm
- D. 52 gm
Explanation: Q = m x c x ΔT where, Q = heat energy required m = mass of the water c = specific heat of water ΔT = change in temperature (final…
Correct answer: 58 gm- A. In bond breaking
- B. In endothermic reactions
- C. In bond formation
- D. Both Options A and B are correct
Explanation: Breaking bonds requires adding energy, the opposite process of forming new bonds always releases energy.
Correct answer: Both Options A and B are correct- A. An endothermic reaction
- B. An exothermic reaction
- C. An isothermic process
- D. A non-spontaneous process
Explanation: This diagram shows a reaction in which the reactants are at a greater energy level than the products, indicating that energy is released…
Correct answer: An exothermic reaction- A. Endothermic reactions
- B. Exothermic reactions
- C. Exergonic reactions
- D. None of these
Explanation: A is correct as in an Endothermic Reaction, the system will absorb heat from the surrounding, hence decreasing its temperature.
Correct answer: Endothermic reactions- A. At constant temperature: Q = -W
- B. When no work is done: ΔU = -W
- C. Work done on the system: ΔU = Q - P Δ V
- D. When work is done by the system: ΔU = Q - W
Explanation: The equation provided in the question follows the first convention, according to which B is not correct.
Correct answer: When no work is done: ΔU = -W- A. 524.1
- B. 41.2
- C. −262.5
- D. −41.2
Explanation: The standard enthalpy change for a reaction can be calculated using the formula: ΔHreaction = ΣΔHf (products) - ΣΔHf (reactants).
Correct answer: 41.2- A. Henry's law
- B. Hess's law
- C. Joule's principle
- D. Dalton's law
Explanation: Hess's Law is a fundamental principle in thermochemistry, asserting that the total enthalpy change during a chemical reaction is the same…
Correct answer: Hess's law- A. -1.91
- B. +2.1
- C. -2.1
- D. +1.91
Explanation: -2.1: This option suggests a negative value for the enthalpy change of graphite, and it is the correct answer.
Correct answer: -1.91- A. -676 kJ mol-1
- B. -110 kJ mol-1
- C. 110 kJ mol-1
- D. 676 kJ mol-1
Explanation: Writing equation 1 as it is and flipping equation 3: 1.C+02--> CO2 H=-393.7 kJ 3.CO2 --> CO +1/2O2 H=+283 kJ Adding these two equations…
Correct answer: -110 kJ mol-1- A. Law of heat summation
- B. 1st law of thermodynamics
- C. Law of increasing entropy
- D. Law of heat exchange
Explanation: Hess's Law is a direct consequence of the First Law of Thermodynamics and the fact that enthalpy is a state function.
Correct answer: 1st law of thermodynamics- A. 1238.78 J mol−1
- B. −2477.57 J mol−1
- C. 2477.57 J mol−1
- D. −1238.78 J mol−1
Explanation: The reaction is C(s) + ½O₂(g) → CO(g). The relationship is ΔH - ΔU = ΔngRT.
Correct answer: 1238.78 J mol−1