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 13 of 37
- A. CH4 + 2O2 → CO2 + 2H2O
- B. C+2S → CS2
- C. H2 + I2 → 2HI
- D. None of the above
Explanation: In an exothermic reaction, energy is released as heat. Option A involves the combustion of methane, which is a highly exothermic process.
Correct answer: CH4 + 2O2 → CO2 + 2H2O- A. C + O2 → CO2
- B. H2 + I2 → 2HI
- C. N2 + 3H2 ⇌ 2NH3
- D. None of the above
Explanation: The correct answer is option B: H2 + I2 → 2HI. This reaction is endothermic because it requires heat to be absorbed for the reaction to…
Correct answer: H2 + I2 → 2HI- A. An exothermic reaction.
- B. An endothermic reaction.
- C. An unbalanced equation.
- D. None of the above.
Explanation: The given reaction C+2S → CS2 with ∆H = +117.5 KJ/mole is endothermic, as indicated by the positive enthalpy change (∆H).
Correct answer: An endothermic reaction.- A. Enthalpy.
- B. Change in enthalpy.
- C. Quantity of heat absorbed.
- D. Quantity of heat evolved.
Explanation: The sign of ΔH represents the change in enthalpy during a chemical reaction.
Correct answer: Change in enthalpy.- A. First law of thermodynamics.
- B. Law of conservation of energy.
- C. Hess's Law.
- D. None of the above
Explanation: The correct answer is Hess's Law. Hess's Law states that the total enthalpy change for a chemical reaction is the same, regardless of…
Correct answer: Hess's Law.- A. It helps in calculating the heat of reaction.
- B. It helps in calculating the heat of combustion.
- C. It helps in calculating the heat of formation.
- D. It tells whether the reaction is exothermic or endothermic.
Explanation: Hess's Law of constant heat summation is a fundamental principle that allows for the calculation of the total enthalpy change of a…
Correct answer: It tells whether the reaction is exothermic or endothermic.- A. An endothermic reaction.
- B. An exothermic reaction.
- C. A process in which no heat changes occur.
- D. A process accompanied by a chemical reaction.
Explanation: Evaporation of water is an endothermic process because it requires energy to overcome the hydrogen bonds between water molecules.
Correct answer: An endothermic reaction.- A. Enthalpy.
- B. Heat energy.
- C. Internal energy.
- D. Combustion energy.
Explanation: The heat content of a system is known as enthalpy, represented by the symbol 'H'.
Correct answer: Enthalpy.- A. Is always negative.
- B. Is always positive.
- C. May be negative or positive.
- D. Is zero.
Explanation: The enthalpy of formation, denoted as Hf, is defined as the change in enthalpy when one mole of a compound is formed from its elements in…
Correct answer: Is zero.- A. Calculating the heat of reaction.
- B. The rate of reaction.
- C. The equilibrium constant.
- D. The effect of pressure on the volume of a gas.
Explanation: Hess's law of constant heat summation states that the total enthalpy change for a reaction is the same, no matter whether the reaction…
Correct answer: Calculating the heat of reaction.- A. Energy can neither be created nor destroyed.
- B. A system may lose energy but that energy will go to the surroundings to increase.
- C. The total energy of the system and its surroundings remains constant.
- D. All the above statements are correct.
Explanation: The correct answer is Option D: All the above statements are correct. This option is correct because statements A, B, and C all accurately…
Correct answer: All the above statements are correct.- A. Heat changes at constant pressure.
- B. Enthalpy.
- C. Pressure changes at normal pressure.
- D. None of the above.
Explanation: The equation qr = ΔH represents heat changes at constant pressure, as ΔH refers to the change in enthalpy, which is the heat absorbed or…
Correct answer: Heat changes at constant pressure.- A. ΔE = E2 - E1
- B. ΔE = PDV
- C. ΔE = q - w
- D. None of the above
Explanation: The first law of thermodynamics is a statement of energy conservation, expressed as ΔE = q - w, where ΔE is the change in internal energy…
Correct answer: ΔE = q - w- A. System
- B. Surroundings
- C. State
- D. All the three above
Explanation: In thermochemistry, the term 'system' is used to denote the specific portion of the universe that is being studied.
Correct answer: System- A. 298K
- B. 273K
- C. 373K
- D. None of the above
Explanation: The standard enthalpy changes are measured under standard conditions, which include a temperature of 298K (25°C).
Correct answer: 298K- A. First law of thermodynamics.
- B. Law of conservation.
- C. Hess's Law.
- D. None of the above.
Explanation: Hess's Law is a fundamental principle in thermochemistry that states the enthalpy change of a chemical reaction is the same regardless of…
Correct answer: Hess's Law.257. 1 Kcal is equal to:
- A. 4.1868 kJ
- B. 1.055 kJ
- C. 3.6 kJ
- D. None of the above
Explanation: The correct answer is 4.1868 kJ. This is because 1 kilocalorie (Kcal) is equivalent to 4.1868 kilojoules (kJ).
Correct answer: 4.1868 kJ- A. Kcal/mole
- B. KJ/mole
- C. kg/mole
- D. None of the above.
Explanation: The correct answer is KJ/mole. In the International System of Units (SI), energy is typically measured in joules.
Correct answer: KJ/mole- A. Open system
- B. Closed system
- C. Isolated system
- D. Heterogeneous system
Explanation: An open system is one where both matter and energy can be exchanged with the surroundings.
Correct answer: Open system260. If only the transfer of energy with the surrounding but not matter is possible, it is known as:
- A. Open system
- B. Closed system
- C. Isolated system
- D. Heterogeneous system
Explanation: The correct answer is Closed system. In thermochemistry, a closed system is defined as one where energy can be transferred to and from the…
Correct answer: Closed system