All Free Chemistry MCQs with Answers
Every Chemistry question in the bank, across all chapters, each with the correct answer and a written explanation. Free and unlimited, with no account needed.
13,720 questions · page 510 of 686
- 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.10183. Sign of ΔH represents:
- 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.10185. Which of the following statements is not correct about Hess's Law of constant heat summation:
- 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.10186. Evaporation of water is:
- 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.10189. Hess's law deals with:
- 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.10196. 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 system10199. 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- A. Open system.
- B. Closed system.
- C. Isolated system.
- D. Heterogeneous system.
Explanation: The correct answer is an Isolated system because it does not allow the transfer of energy or matter between the system and its…
Correct answer: Isolated system.