1. The First Law of Thermodynamics is a statement of:
A. Conservation of energy
B. Conservation of mass
C. Conservation of momentum
D. Law of definite proportions
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Answer: A. Conservation of energy
Explanation: The First Law states that energy can neither be created nor destroyed, only transformed from one form to another (ΔU = q + w).
2. A system which can exchange neither energy nor matter with its surroundings is called:
A. An isolated system
B. A closed system
C. An open system
D. An adiabatic system
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Answer: A. An isolated system
Explanation: An isolated system has boundary walls that prevent both matter transfer and heat exchange with surroundings.
3. Which of the following is an intensive property?
A. Temperature
B. Mass
C. Volume
D. Enthalpy
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Answer: A. Temperature
Explanation: Intensive properties are independent of the amount of substance present in the system.
4. For a process occurring at constant pressure, heat exchanged (q_p) is equal to:
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Answer: A. ΔH
Explanation: Enthalpy change (ΔH) represents the heat absorbed or evolved by a system at constant pressure.
5. The mathematical expression for the relation between ΔH and ΔU for ideal gases is:
A. ΔH = ΔU + Δn_g RT
B. ΔH = ΔU - Δn_g RT
C. ΔU = ΔH + Δn_g RT
D. ΔH = ΔU / RT
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Answer: A. ΔH = ΔU + Δn_g RT
Explanation: For chemical reactions involving gases, ΔH = ΔU + Δ(PV) = ΔU + Δn_g RT where Δn_g is the change in moles of gaseous species.
6. For an isothermal expansion of an ideal gas, internal energy change (ΔU) is:
A. Zero
B. Positive
C. Negative
D. Infinite
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Answer: A. Zero
Explanation: Internal energy of an ideal gas depends solely on temperature (T). Since ΔT = 0 in an isothermal process, ΔU = 0.
7. A reaction is always spontaneous at all temperatures if:
A. ΔH < 0 and ΔS > 0
B. ΔH > 0 and ΔS < 0
C. ΔH > 0 and ΔS > 0
D. ΔH < 0 and ΔS < 0
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Answer: A. ΔH < 0 and ΔS > 0
Explanation: In ΔG = ΔH - TΔS, if ΔH is negative and ΔS is positive, ΔG will remain negative at any temperature.
8. Hess's Law of constant heat summation is based on:
A. First Law of Thermodynamics
B. Second Law of Thermodynamics
C. Third Law of Thermodynamics
D. Zeroth Law of Thermodynamics
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Answer: A. First Law of Thermodynamics
Explanation: Hess's Law is a consequence of the conservation of energy, stating that overall enthalpy change is independent of the pathway taken.
9. The standard enthalpy of formation (Δ_f H°) of an element in its reference standard state is:
A. Zero
B. Positive
C. Negative
D. Dependent on pressure
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Answer: A. Zero
Explanation: By convention, standard enthalpy of formation of an element in its most stable physical state at 1 bar and 298 K is taken as zero.
10. The unit of entropy (S) is:
A. J K⁻¹ mol⁻¹
B. J mol⁻¹
C. kJ mol⁻¹
D. J K mol⁻¹
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Answer: A. J K⁻¹ mol⁻¹
Explanation: Entropy is defined as heat divided by absolute temperature (S = q/T), giving units of J K⁻¹ mol⁻¹.
11. In an adiabatic process, which of the following is true?
A. q = 0
B. ΔT = 0
C. w = 0
D. ΔP = 0
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Answer: A. q = 0
Explanation: An adiabatic process occurs with no heat transfer between system and surroundings (q = 0).
12. The Third Law of Thermodynamics states that the entropy of a perfectly crystalline substance approaches zero as temperature approaches:
A. Absolute Zero (0 K)
B. 0 °C
C. 273 K
D. 100 °C
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Answer: A. Absolute Zero (0 K)
Explanation: At 0 Kelvin, molecular motion completely ceases in a perfect crystal, causing entropy to drop to zero.
13. Which of the following state functions is used to measure degree of randomness or disorder?
A. Entropy
B. Enthalpy
C. Internal energy
D. Work done
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Answer: A. Entropy
Explanation: Entropy (S) directly quantifies thermal disorder and chaotic motion within a thermodynamic system.
14. For a spontaneous process at constant temperature and pressure, Gibbs free energy change (ΔG) must be:
A. Negative (< 0)
B. Positive (> 0)
C. Zero (= 0)
D. Infinite
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Answer: A. Negative (< 0)
Explanation: A process occurs spontaneously only if Gibbs free energy decreases (ΔG < 0).
15. Work done in a free expansion of an ideal gas in vacuum is:
A. Zero
B. Maximum
C. Positive
D. Negative
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Answer: A. Zero
Explanation: Free expansion occurs against external pressure P_ext = 0, so work done w = -P_ext ΔV = 0.
16. The condition for equilibrium in a reversible reaction in terms of ΔG is:
A. ΔG = 0
B. ΔG < 0
C. ΔG > 0
D. ΔG = 1
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Answer: A. ΔG = 0
Explanation: When a system reaches thermodynamic equilibrium, there is no driving force, hence ΔG = 0.
17. Which of the following is NOT a state function?
A. Heat (q)
B. Enthalpy (H)
C. Entropy (S)
D. Internal Energy (U)
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Answer: A. Heat (q)
Explanation: Heat (q) and Work (w) are path functions because their values depend on the path taken between states.
18. Heat capacity at constant volume is denoted by C_v. The relation C_p - C_v for 1 mole of an ideal gas is:
A. R
B. 2R
C. R / 2
D. Zero
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Answer: A. R
Explanation: Mayer's relation states C_p - C_v = R for one mole of an ideal gas.
19. In an endothermic reaction, enthalpy change (ΔH) is always:
A. Positive
B. Negative
C. Zero
D. Equal to ΔS
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Answer: A. Positive
Explanation: Endothermic processes absorb heat from surroundings, increasing the enthalpy of products over reactants (ΔH > 0).
20. The change in entropy when ice melts to form liquid water at 0 °C is:
A. Positive
B. Negative
C. Zero
D. Undefined
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Answer: A. Positive
Explanation: Transition from a rigid crystalline solid to a fluid liquid increases molecular mobility and disorder (ΔS > 0).
21. Bomb calorimeter is used to measure heat change at:
A. Constant volume (q_v)
B. Constant pressure (q_p)
C. Constant temperature
D. Variable volume
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Answer: A. Constant volume (q_v)
Explanation: A bomb calorimeter has a rigid, sealed steel vessel maintaining constant volume during combustion reactions (q_v = ΔU).
22. Bond dissociation energy is always:
A. Positive
B. Negative
C. Zero
D. Dependent on temperature only
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Answer: A. Positive
Explanation: Breaking chemical bonds requires energy input, making bond dissociation an endothermic process (ΔH > 0).
23. Which statement represents the Zeroth Law of Thermodynamics?
A. Defines concept of temperature and thermal equilibrium
B. Conservation of energy
C. Concept of entropy
D. Absolute zero entropy
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Answer: A. Defines concept of temperature and thermal equilibrium
Explanation: If two bodies are in thermal equilibrium with a third body, they are in thermal equilibrium with each other.
24. Standard state conditions for thermodynamic measurements are:
A. 1 bar pressure and specified temperature (usually 298.15 K)
B. 1 atm pressure and 0 K
C. 100 bar pressure and 273 K
D. 1 bar pressure and 0 °C
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Answer: A. 1 bar pressure and specified temperature (usually 298.15 K)
Explanation: The IUPAC standard state specifies a pressure of 1 bar at 298.15 K (25 °C).
25. An extensive property among the following is:
A. Volume
B. Density
C. Pressure
D. Refractive index
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Answer: A. Volume
Explanation: Extensive properties depend on the mass or quantity of matter present in the system.
26. In an exothermic reaction, heat is evolved. Therefore, ΔH is:
A. Negative
B. Positive
C. Zero
D. Equal to ΔU + RT
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Answer: A. Negative
Explanation: Exothermic reactions release energy into the surroundings, causing system enthalpy to decrease (ΔH < 0).
27. Relation between standard free energy change (ΔG°) and equilibrium constant (K) is:
A. ΔG° = -RT ln K
B. ΔG° = RT ln K
C. ΔG° = -RT log K
D. ΔG° = RT / K
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Answer: A. ΔG° = -RT ln K
Explanation: Thermodynamically, standard free energy change is linked to equilibrium constant via ΔG° = -RT ln K = -2.303 RT log K.
28. Thermochemistry is mainly concerned with the study of:
A. Heat changes during chemical reactions
B. Rates of reaction
C. Movement of ions
D. Atomic structures
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Answer: A. Heat changes during chemical reactions
Explanation: Thermochemistry deals with the heat energy absorbed or released during chemical transformations.
29. The unit of molar heat capacity is:
A. J K⁻¹ mol⁻¹
B. J K⁻¹
C. J mol⁻¹
D. kJ K⁻¹
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Answer: A. J K⁻¹ mol⁻¹
Explanation: Molar heat capacity is the amount of heat required to raise the temperature of 1 mole of substance by 1 Kelvin.
30. For the sublimation of solid iodine (I₂ (s) → I₂ (g)), the signs of ΔH and ΔS are respectively:
A. Positive and Positive
B. Negative and Negative
C. Positive and Negative
D. Negative and Positive
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Answer: A. Positive and Positive
Explanation: Sublimation requires heat absorption (ΔH > 0) and increases spatial disorder going from solid to gas (ΔS > 0).
