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 23 of 37
- A. 58 gm
- B. 56 gm
- C. 54 gm
- D. 52 gm
Explanation: First, let's calculate the heat required to raise the temperature of water from 30°C to 100°C: Heat (Q) = mass (m) × specific heat (c) ×…
Correct answer: 58 gm- A. ∆H is always less than ∆E .
- B. ∆H is always greater than ∆E .
- C. ∆H is less than ∆E if the number of moles of gaseous products is greater than the number of moles of gaseous reactants.
- D. ∆H is less than ∆E if the number of moles of gaseous products is less than the number of moles of gaseous reactants.
Explanation: As ∆H =∆E + ∆n0RT ∆H value is less than or greater than ∆E depending on the value of ∆ngwhich is the change in number of moles of the…
Correct answer: ∆H is less than ∆E if the number of moles of gaseous products is less than the number of moles of gaseous reactants.443. Which of the following thermodynamic quantities is an outcome of the second law of thermodynamics?
- A. Work
- B. Enthalpy
- C. Internal energy
- D. Entropy
Explanation: The entropy concept is direct outcome of the second law of thermodynamics through the Carnot cycle approach.
Correct answer: Entropy- A. PΔV
- B. -PΔV
- C. PV
- D. ΔPV
Explanation: Work done by the system is considered negative. (W=-PΔV)
Correct answer: -PΔV- A. Enthalpy
- B. Work
- C. Internal energy
- D. Kinetic energy
Explanation: Enthalpy is a thermodynamic property of a system, denoted by the symbol H.
Correct answer: Enthalpy- A. Positive
- B. Negative
- C. Either positive or negative
- D. None of the above
Explanation: Enthalpy of formation may be negative or positive. Mg(s) +1/2O2 → MgO(s) ΔHº f = -692kj / mol 1/2 N2(g) O2(g) → No2(g) ΔHº f = 33.18kj / mol
Correct answer: Either positive or negative- A. Heat content
- B. Rate of reaction
- C. Internal energy
- D. Activation energy
Explanation: Total heat content of the system is called enthalpy. Enthalpy is a thermodynamic property of a system, denoted by the symbol H.
Correct answer: Heat content- A. Fe(g)
- B. C(l)
- C. Cu(s)
- D. Na(g)
Explanation: Standard enthalpy of an element in its standard state is zero. Copper is a solid in standard form.
Correct answer: Cu(s)- A. Its value gives an idea about the relative stability of reactants and the products
- B. It is always negative
- C. Value depends upon nature of bonds
- D. Its value may be negative or positive
Explanation: The standard enthalpy of formation of a compound is the amount of heat absorbed or evolved when one mole of compound is formed from its…
Correct answer: It is always negative- A. Neutralization
- B. Combustion
- C. Atomization
- D. All of the above
Explanation: Enthalpy of neutralization & enthalpy of combustion are always negative while enthalpy of atomization is always positive.
Correct answer: Atomization- A. Enthalpy of reaction
- B. Enthalpy of formation
- C. Enthalpy of neutralization
- D. Enthalpy of combustion
Explanation: The standard enthalpy of neutralization is the amount of heat evolved when one mole of H+ ions from an acid react with one mole of OH-…
Correct answer: Enthalpy of neutralization- A. 0°C and 1 atm pressure
- B. 0 K and 1 atm pressure
- C. 25°C and 1 atm pressure
- D. 25°C and 2 atm pressure
Explanation: Standard conditions for enthalpy measurement are given below:Temperature =25°C (298 K), Pressure= 1 atm (760 torr).
Correct answer: 25°C and 1 atm pressure- A. 50 kJ
- B. 100 kJ
- C. 150 kJ
- D. 5000 kJ
Explanation: It's calculated by subtracting the work done on the surroundings from the heat absorbed by the system.
Correct answer: 50 kJ- A. 84,000 J
- B. -2000/4.2 J
- C. 2000/4.2 J
- D. -8400 J
Explanation: q=mxsxΔT =100x4.2x20=8400=-8400 JIt accurately represents the heat evolved when the temperature of the water decreases.
Correct answer: -8400 J- A. ΔΗlatt = ΔΗf- ΔΗx
- B. ΔΗlatt = ΔΗf + ΔΗx
- C. ΔΗlatt = ΔΗa + ΔΗv
- D. ΔΗlatt = ΔΗf - ΔΗsol
Explanation: Option A is correct.The correct relationship to determine the lattice energy of an ionic compound is:ΔHlatt =ΔHf − ΔHx ΔHf is the heat of…
Correct answer: ΔΗlatt = ΔΗf- ΔΗx- A. Na(s) + 1/2 Cl2(g) → NaCl(s)
- B. Na˕(aq) + Cl-(aq) → NaCl(aq)
- C. Na(s) + Cl(g) → NaCl(s)
- D. Na˕(g) + Cl-(g) → NaCl(s)
Explanation: Option D is correct.The equation that shows lattice energy for an ionic compound is: Na ˕ (g) + Cl ⁻ (g) → NaCl(s) This equation shows the…
Correct answer: Na˕(g) + Cl-(g) → NaCl(s)- A. ∆H°latt for ionic compound
- B. ∆H° f for CO(g)
- C. ∆H°f for B2O3
- D. All of these
Explanation: The enthalpy of formation of an ionic compound cannot be measured directly.
Correct answer: All of these- A. +1258 kJ mol-1
- B. +180 kJ mol-1
- C. -184 kJ mol-1
- D. -680 kJ mol-1
Explanation: Option C is correct.The standard enthalpy change of formation of propyne, CH3CCH is -184 kJ/mol.
Correct answer: -184 kJ mol-1- A. -3.37 kcal
- B. +3.37 kcal
- C. -33.7 kcal
- D. 33.7 kcal
Explanation: Option C is correct.The heat of combustion of ethane (C2H6) is -337.0 kcal at 25°C.
Correct answer: -33.7 kcal- A. Spontaneous
- B. Decomposition
- C. Non-spontaneous
- D. Hydrolysis
Explanation: Option a is correct because the evaporation of water is a process that occurs naturally without requiring an external input of energy.
Correct answer: Spontaneous