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 6 of 37
- A. Molecular size
- B. Pressure only.
- C. Volume only
- D. Temperature only
Explanation: In an ideal gas, the inter-molecular collisions are assumed to be absent and the collisions are perfectly elastic.
Correct answer: Temperature only- A. 50 kJ
- B. 100 kJ
- C. 150 kJ
- D. 5000 kJ
Explanation: According to the first law of thermodynamics, ΔU = q + w. Heat absorbed is positive (q = +100 kJ), and work done by the system is negative…
Correct answer: 50 kJ- A. 3/2R
- B. 5/2R
- C. Dependent on the atomicity of the gas
- D. Infinity
Explanation: When a gas is at constant temperature and pressure, adding heat does not change the temperature, which means the heat capacity is…
Correct answer: Infinity- A. Endothermic
- B. Exothermic
- C. ∆H = 0
- D. None of the above
Explanation: The enthalpy of reaction is ΔH = ΣΔHf (products) - ΣΔHf (reactants). ΔH = [4(0) + 3(-393.7)] - [2(-824.2) + 3(0)] = -1181.1 + 1648.4 =…
Correct answer: Endothermic- A. 70.26 JK-1
- B. 82.55 JK-1
- C. 95.73 JK-1
- D. 107.11 JK-1
Explanation: To calculate the change in entropy of an ideal gas, we can use the formula:ΔS = nR ln(V2/V1)Given that 5 moles of an ideal gas expand…
Correct answer: 95.73 JK-1- A. Extensive property
- B. Colligative property
- C. Intensive property
- D. Constitutive property
Explanation: Standard heat of combustion is defined for a specific amount of substance (per mole).
Correct answer: Intensive property- A. 20 ml acid and 30 ml alkali
- B. 10 ml acid and 40 ml alkali
- C. 25 ml acid and 25 ml alkali
- D. 35 ml acid and 15 ml alkali
Explanation: The heat released is maximized when the maximum number of moles of acid and base react.
Correct answer: 25 ml acid and 25 ml alkali- A. ∆S > 0
- B. ∆S < 0
- C. ∆H < 0
- D. ∆G > 0
Explanation: As ∆G = ∆H - T∆SFor spontaneous process, ∆G = negative For endothermic process, ∆H = positive Therefore, ∆S > 0
Correct answer: ∆S > 0- A. Adiabatic expansion
- B. Adiabatic compression
- C. Both a and b
- D. None of these
Explanation: In an adiabatic expansion, the gas expands without heat exchange with the surroundings, leading to a decrease in internal energy and…
Correct answer: Adiabatic expansion- A. ΔH
- B. ΔE
- C. ΔV
- D. ΔH+ΔE
Explanation: The change in enthalpy (ΔH) of a system is defined as the heat transferred at constant pressure.
Correct answer: ΔH- A. Heat of reaction
- B. Heat of atomization
- C. Heat of formation
- D. Heat of combustion
Explanation: This is the precise definition of the standard enthalpy of combustion (ΔH°c ).
Correct answer: Heat of combustion- A. ΔHf (formation)
- B. ΔHc (combustion)
- C. ΔHsol (solution)
- D. Both A and C
Explanation: The enthalpy of formation (ΔHf) can be positive (endothermic) or negative (exothermic).
Correct answer: Both A and C- A. Spontaneous
- B. Exothermic
- C. Non-spontaneous
- D. Both A and B
Explanation: The reaction between a strong acid and a strong base is highly favorable, releasing a significant amount of heat (exothermic, ΔH < 0).
Correct answer: Both A and B- 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: The symbol "°" denotes standard conditions in thermodynamics. For thermochemical data, this is almost universally defined as a pressure of…
Correct answer: 25°C and 1 atm pressure- A. ΔH=ΔU+PΔV
- B. ΔH=ΔU-ΔnRT
- C. ΔU=ΔH+ΔP
- D. ΔH=ΔU-PΔV
Explanation: This equation is the definition of enthalpy change (ΔH) at constant pressure.
Correct answer: ΔH=ΔU+PΔV- A. 1/2 I(sp)→ I(l)
- B. 1/2 I2(s)→I(g)
- C. I2(l)→2l(g)
- D. I2(g)→2l(g)
Explanation: The standard enthalpy of atomization of an element is the amount of heat absorbed when one mole of gaseous atoms are formed from the…
Correct answer: 1/2 I2(s)→I(g)- A. 273 K
- B. 373 K
- C. 298 K
- D. 473 K
Explanation: The standard enthalpy of formation, ΔH°f, is measured under standard conditions, which include a temperature of 25°C (298 K) and a…
Correct answer: 298 K- A. Enthalpy of solution
- B. Enthalpy of sublimation
- C. Enthalpy of neutralization
- D. Enthalpy of formation
Explanation: The reaction between an acid and a base to form a salt and water is an exothermic process, meaning it always releases heat.
Correct answer: Enthalpy of neutralization- A. Law of heat summation
- B. Law of constant heat capacity
- C. Law of mass action
- D. Law of conservation of mass
Explanation: Hess's law of heat summation, also known as Hess's law, states that the enthalpy change for a chemical reaction is the same whether the…
Correct answer: Law of heat summation- A. Joule mol-1
- B. KJ mol-1
- C. Both A and B
- D. None of these
Explanation: The SI unit for energy change in a chemical reaction is joules per mole.
Correct answer: Both A and B