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 31 of 37
601. I k cal is equal to
- A. 41.8 x 10^3 J
- B. 418 x 10^3 J
- C. 4.18 x 10^3 J
- D. 0.418 x 10^3 J
Explanation: The correct conversion factor between calories and joules is 1 cal = 4.18 J.
Correct answer: 4.18 x 10^3 J- A. Q
- B. Q - W
- C. Q / W
- D. Q + Q
Explanation: The correct answer is Q - W, which corresponds to the change in internal energy (∆E) of a system.
Correct answer: Q - W- A. ∆Hfusion is positive only
- B. ∆H aq is positive only
- C. ∆Hn is negative only
- D. ∆Hsoln is negative only
Explanation: The enthalpy of solution (∆Hsoln) can be either positive or negative. It is incorrect to state it is negative only, as dissolution can be…
Correct answer: ∆Hsoln is negative only- A. -217.4 kJ
- B. -119 kJ
- C. +217.4 kJ
- D. +119 kJ
Explanation: To find the heat of formation of PCl5, we need to add the enthalpy changes of the given reactions.
Correct answer: +119 kJ- A. (y - 2x)
- B. (x + y)
- C. (2x -y)
- D. 2x/y
Explanation: Reverse the second reaction and change the sign of its enthalpy change: SO3(g) + y kJ → SO2(g) + 1/2 O2(g) Multiply the first reaction by…
Correct answer: (2x -y)- A. 4
- B. 27
- C. 4/27
- D. 1/27
Explanation: To find the equilibrium constant Kp for the reaction NH4COONH2(s) <-> 2NH3(g) + CO2(g), we use the formula Kp = PNH3^2 * PCO2 where P…
Correct answer: 4- A. Tf > Ti for reversible process but Tf = Ti for irreversible process.
- B. (Tf)rev = (Tf)irrev
- C. Tf = Ti for both reversible and irreversible processes
- D. (Tf)irrev > (Tf)rev
Explanation: In an isolated system, the expansion of an ideal gas occurs adiabatically, meaning no heat is exchanged with the surroundings (q = 0).
Correct answer: (Tf)irrev > (Tf)rev- A. the internal energy changes in all processes
- B. internal energy and entropy are state functions
- C. the change in entropy can never be 0
- D. the work done an adiabatic process is always 0
Explanation: This statement is generally true. State functions depend only on the current state of a system (its thermodynamic state), not on the path…
Correct answer: internal energy and entropy are state functions- A. Entropy
- B. Internal energy
- C. Volume
- D. Density
Explanation: Density is not a state variable of thermodynamics because it depends on both the state variables of volume and mass.
Correct answer: Density- A. Amount of heat added to the system
- B. Amount of heat rejected from the system
- C. The temperature of the substance
- D. Amount of the substance
Explanation: The change in entropy is defined as ΔS = ΔQ/T, where ΔQ is the heat transfer and T is the temperature.
Correct answer: Amount of the substance- A. Decreases
- B. Increases
- C. Remains the same
- D. Both A and B
Explanation: The energy of the universe increases because energy never flows uphill spontaneously.
Correct answer: Increases- A. Boiling point
- B. Molarity
- C. Freezing point
- D. All of the above
Explanation: An intensive property does not change with the size or amount of the sample; it is inherent to the substance itself.
Correct answer: All of the above- A. Double of the original value
- B. Half of the original value
- C. Remain the same as the original value
- D. One-fourth of the original value
- E. Heat of formation
Explanation: Thermodynamic properties can be divided into two general classes, intensive and extensive properties.
Correct answer: Half of the original value- A. Temperature
- B. Volume
- C. Quantity
- D. Pressure
Explanation: Mass and volume are examples of extensive properties. An intensive property is a property of matter that depends only on the type of…
Correct answer: Quantity- A. The reaction proceeds in the forward direction at 300 K
- B. At 1200 K, reaction proceeds in the reverse direction
- C. At 300 K, Kp > 1
- D. At 300 K, the products will be favoured more than reactants at equilibrium
Explanation: This is the following solution: kp is less than one, reaction is non spontaneous for sponataneous reactions kp is greater than one
Correct answer: At 300 K, Kp > 1- A. The thermodynamics first law is not sufficient to predict the direction of the process
- B. In the case of an exothermic reaction, the overall enthalpy fo the products is greater than that of reactants
- C. for the reaction H2(g) + Br2 (l) → 2HBr (g) from the bond enthaly data, It is possible to calculate the value of H
- D. At 298K and 1 atmpressure, diamond's standard enthalpy is zero
Explanation: Only option A has correct statement. The first law of thermodynamics states that energy is conserved in any process.
Correct answer: The thermodynamics first law is not sufficient to predict the direction of the process- A. q = H at constant T; q = E at constant V
- B. q = H at constant V; q = E at constant P
- C. q = H at constant P; q = E at constant V
- D. q = H = E at constant P or at constant V
Explanation: q = H = E at constant P or at constant V: This statement is true. At constant pressure (P) or constant volume (V), the heat transfer (q)…
Correct answer: q = H = E at constant P or at constant V- A. Change in state of the system may occur
- B. Temperature of the system may rise
- C. Chemical reaction may take place
- D. All
Explanation: Explanation: An increase in internal energy can lead to various changes, including changes in state, a rise in temperature, and potential…
Correct answer: All- A. K
- B. KCal
- C. Cal
- D. GJ
Explanation: Explanation: The unit of heat in the SI system is the calorie (Cal).
Correct answer: Cal- A. qp>qv
- B. delta E<Delta H
- C. delta E>Delta H
- D. Both a & b
Explanation: Explanation: Both statements are correct. ΔE represents the change in internal energy and can be less than ΔH in some instances…
Correct answer: Both a & b