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 10 of 37
- A. Thermal energy is converted into kinetic energy of water molecules
- B. Pressure of water molecules increases
- C. The piston is pushed up
- D. All of the above
Explanation: This is the correct answer. Let's break down why each individual option is true:Thermal energy is converted into kinetic energy of water…
Correct answer: All of the above- A. More CO2 and H2 are produced to compensate for temperature change
- B. The reaction will move in backward direction for compensation
- C. No change will take place
- D. The reaction will stop
Explanation: When heat is applied to a system at equilibrium, Le Chatelier's principle states that the system will adjust to counteract the change and…
Correct answer: The reaction will move in backward direction for compensation- A. I only
- B. II only
- C. Both (I) and (II) are correct
- D. Neither (I) nor (II) are correct
Explanation: In the open beaker, H₂ gas is produced, and work is done by the system against the constant atmospheric pressure (W = -ΔngRT).
Correct answer: Both (I) and (II) are correct- A. -98 kJ/mol
- B. 98 kJ/mol
- C. 14 kJ/mol
- D. 24 kJ/mol
Explanation: The neutralization of a weak acid releases less heat because some energy is used to dissociate the acid first.
Correct answer: 14 kJ/mol- A. -40 kJ/mol
- B. +33 kJ/mol
- C. -45 kJ/mol
- D. -6 kJ/mol
Explanation: The standard enthalpy of formation (ΔH°) of nitrogen dioxide (NO₂) is a known endothermic value.
Correct answer: +33 kJ/mol- A. - 342 kJ/mol
- B. - 234 kJ/mol
- C. - 346 kJ/mol
- D. - 178 kJ/mol
Explanation: The neutralization reaction is H⁺(aq) + OH⁻(aq) → H₂O(l). The enthalpy change is ΔHneut = ΔHf (H₂O) - [ΔHf (H⁺) + ΔHf (OH⁻)].
Correct answer: - 234 kJ/mol- A. 100 gm
- B. 180 gm
- C. 200 gm
- D. 120 gm
Explanation: First, calculate the work done: W = mgh = 100 kg × 10 m/s² × 500 m = 500,000 J.
Correct answer: 120 gm- A. Boiling point
- B. Molarity
- C. Freezing point
- D. All
Explanation: An intensive property is a property of a system that does not depend on the amount of substance.
Correct answer: All- A. 58 gm
- B. 56 g
- C. 54 g
- D. 52 g
Explanation: First, calculate the heat required to warm the water: Q = mcΔT = (10,000 g)(1 cal/g°C)(70°C) = 700,000 cal = 700 kcal.
Correct answer: 58 gm- A. 4q3 − q1 − 2q2
- B. q1 + q2 − q3
- C. q1 + 2q2 − 4q3
- D. q1 + 4q2 − 4q3
Explanation: The enthalpy of formation is calculated as the energy required to break bonds minus the energy released from forming bonds.
Correct answer: q1 + 2q2 − 4q3- A. -1.91
- B. +2.1
- C. -2.1
- D. +1.9
Explanation: Here, we can use the equation: ΔH (graphite → diamond) = ΔH (graphite → CO₂) - ΔH (diamond → CO₂) ΔH = -393.51 kJ mol⁻¹ - (-395.41 kJ…
Correct answer: +1.9- A. -228.88 KJ/mol
- B. -343.52 KJ/mol
- C. +228.88 KJ/mol
- D. -22.88 KJ/mol
Explanation: For the formation of H⁺ ions from hydrogen and O₂⁻ ions from oxygen, the standard enthalpy of formation at 25°C is -228.88 KJ/mol.
Correct answer: -228.88 KJ/mol- A. A
- B. B
- C. C
- D. D
Explanation: N₂(g) + O₂(g) → 2NO(g) is endothermic, meaning it absorbs heat from its surroundings (it has a positive ΔH value, around +180.6 kJ/mol).
Correct answer: C- A. -5.3 kJ
- B. -44.7 kJ
- C. +5.3 kJ
- D. +44.7 kJ
Explanation: ΔG = ΔH - TΔS = -50000 - 298 × (-150) = -50000 + 44700 = -5300 J = -5.3 kJ.
Correct answer: -5.3 kJ- A. -67800 cal
- B. -67650.4 cal
- C. -67762.5 cal
- D. -54.6 cal
Explanation: Calculate ΔCp (Change in Heat Capacity): Reaction: CO(g) + 1/2 O2(g) → CO2(g). ΔCp = Cp(Products) - ΣCp(Reactants).
Correct answer: -67800 cal- A. Always less than lattice energy
- B. Same as lattice energy
- C. Always greater than lattice energy
- D. May or may not be same as lattice energy
Explanation: Enthalpy of formation (ΔHf) includes lattice energy (LE) plus the additional enthalpy changes needed to form ions from their elements…
Correct answer: Always greater than lattice energy- A. Heat of reaction
- B. Spontaneity of reaction
- C. Rate of reaction
- D. Entropy of reaction
Explanation: Thermodynamics describes the energy changes directly whereas entropy changes and spontaneity of a reaction are explained through derived…
Correct answer: Rate of reaction- A. Remain constant
- B. Increase
- C. Either increase or decrease
- D. Decrease
Explanation: An endothermic reaction absorbs heat from its surroundings to proceed. If the reaction is rapid, it will quickly draw heat from the…
Correct answer: Decrease- A. Evaporation
- B. Sublimation
- C. Respiration
- D. Boiling
Explanation: Respiration is the metabolic process where organisms break down glucose and oxygen to produce carbon dioxide, water, and energy.
Correct answer: Respiration- A. Isothermal process
- B. Spontaneous
- C. Non-spontaneous
- D. Adiabatic process
Explanation: A spontaneous process is a process that occurs in a system without the need for external energy input.
Correct answer: Spontaneous