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NUMS Chemistry — States of Matter, Energetics and Equilibria (Set 7)

Take the NUMS Chemistry — States of Matter, Energetics and Equilibria (Set 7): 30 multiple-choice questions (40 minutes) with instant scoring and a full…

What this test covers

• 30 NUMS Chemistry

Sample questions with answers

The first 5 questions of this test, with the correct answer and explanation.

1. Q1. Taking R = 0.0821 dm³ atm K⁻¹ mol⁻¹, what is the density of ammonia gas (NH₃ = 17) at 27 °C and 2.00 atm, assuming ideal behaviour?

   • A. 0.34 g dm⁻³
   • B. 2.76 g dm⁻³
   • C. 1.38 g dm⁻³ ✓
   • D. 0.69 g dm⁻³

   Answer: C. 1.38 g dm⁻³

   Explanation: d = PM/RT = (2.00 × 17)/(0.0821 × 300) = 1.38 g dm⁻³.

2. Q2. A gas X effuses through a small hole in 45 s, while the same volume of oxygen (M = 32) takes 30 s under identical conditions. What is the molar mass of X?

   • A. 21 g mol⁻¹
   • B. 96 g mol⁻¹
   • C. 48 g mol⁻¹
   • D. 72 g mol⁻¹ ✓

   Answer: D. 72 g mol⁻¹

   Explanation: t ∝ √M, so M(X) = 32 × (45/30)² = 32 × 2.25 = 72 g mol⁻¹.

3. Q3. A 10.0 dm³ vessel at 27 °C holds 3.2 g CH₄, 4.4 g CO₂ and 2.8 g N₂ (C = 12, H = 1, O = 16, N = 14). What is the total pressure, with R = 0.0821 dm³ atm K⁻¹ mol⁻¹?

   • A. 0.492 atm
   • B. 0.985 atm ✓
   • C. 0.246 atm
   • D. 1.97 atm

   Answer: B. 0.985 atm

   Explanation: n = 0.20 + 0.10 + 0.10 = 0.40 mol; P = nRT/V = 0.40 × 0.0821 × 300/10 = 0.985 atm.

4. Q4. A gas cylinder holds 2.0 g of hydrogen and 8.0 g of helium (H = 1, He = 4) at a total pressure of 3.0 atm. What is the partial pressure of helium?

   • A. 1.0 atm
   • B. 2.4 atm
   • C. 2.0 atm ✓
   • D. 0.75 atm

   Answer: C. 2.0 atm

   Explanation: n(H₂) = 1.0 mol, n(He) = 2.0 mol; x(He) = 2/3; p(He) = (2/3) × 3.0 = 2.0 atm.

5. Q5. 100 mL of hydrogen is collected over water at 25 °C when the barometer reads 760 torr (vapour pressure of water at 25 °C = 23.8 torr). What volume would the dry hydrogen occupy at 760 torr and 0 °C? (R = 0.0821 dm³ atm K⁻¹ mol⁻¹)

   • A. 88.7 mL ✓
   • B. 90.6 mL
   • C. 100 mL
   • D. 96.8 mL

   Answer: A. 88.7 mL

   Explanation: p(H₂) = 736.2 torr; V₀ = 100 × (736.2/760) × (273.15/298.15) = 88.7 mL.

The other 25 questions

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6. Q6. What is the root-mean-square speed of methane molecules (M = 16 g mol⁻¹) at 27 °C? (R = 8.314 J K⁻¹ mol⁻¹; use M in kg mol⁻¹)

   • A. 684 m s⁻¹
   • B. 484 m s⁻¹
   • C. 21.6 m s⁻¹
   • D. 1367 m s⁻¹

7. Q7. From ΔH°c(C, graphite) = −393.5, ΔH°c(H₂) = −285.8 and ΔH°c(CH₄) = −890.3 kJ mol⁻¹, what is ΔH°f of methane?

   • A. −211.0 kJ mol⁻¹
   • B. −74.8 kJ mol⁻¹
   • C. +74.8 kJ mol⁻¹
   • D. −1569.4 kJ mol⁻¹

8. Q8. Using bond enthalpies (kJ mol⁻¹) H–H 436, Cl–Cl 243 and H–Cl 431, what is ΔH for H₂(g) + Cl₂(g) → 2HCl(g)?

   • A. −183 kJ mol⁻¹
   • B. +183 kJ mol⁻¹
   • C. −862 kJ mol⁻¹
   • D. −92 kJ mol⁻¹

9. Q9. 50.0 mL of 1.00 M HCl is mixed with 50.0 mL of 1.00 M NaOH in a polystyrene cup and the temperature rises by 6.8 °C. Taking the density as 1.00 g mL⁻¹ and c = 4.18 J g⁻¹ K⁻¹ for the mixture, what is ΔH of neutralisation per mole of water formed?

   • A. −2.84 kJ mol⁻¹
   • B. −113.7 kJ mol⁻¹
   • C. −56.8 kJ mol⁻¹
   • D. −28.4 kJ mol⁻¹

10. Q10. For 2SO₂(g) + O₂(g) → 2SO₃(g) at 300 K, ΔH = −198.0 kJ. What is ΔU for the reaction? (R = 8.314 J K⁻¹ mol⁻¹)

    • A. −200.5 kJ
    • B. −195.5 kJ
    • C. −198.0 kJ
    • D. −193.0 kJ

11. Q11. 1.00 mol each of H₂ and I₂ are placed in a 1.00 dm³ flask at a temperature where Kc = 50.0 for H₂ + I₂ ⇌ 2HI. What is the equilibrium concentration of HI?

    • A. 1.00 mol dm⁻³
    • B. 1.56 mol dm⁻³
    • C. 1.78 mol dm⁻³
    • D. 0.78 mol dm⁻³

12. Q12. N₂O₄(g) ⇌ 2NO₂(g) is 20% dissociated at a total pressure of 1.00 atm. What is Kp in atm?

    • A. 0.167
    • B. 0.200
    • C. 0.667
    • D. 0.040

13. Q13. For CaCO₃(s) ⇌ CaO(s) + CO₂(g) at 800 °C (1073 K), the equilibrium pressure of CO₂ is 0.220 atm. What is Kc in mol dm⁻³? (R = 0.0821 dm³ atm K⁻¹ mol⁻¹)

    • A. 2.50 × 10⁻³
    • B. 0.62 × 10⁻³
    • C. 18.1 × 10⁻³
    • D. 0.220

14. Q14. The solubility product of Mg(OH)₂ is 1.8 × 10⁻¹¹ mol³ dm⁻⁹ at 25 °C. What is the pH of a saturated solution (Kw = 1.0 × 10⁻¹⁴)?

    • A. 3.48
    • B. 9.78
    • C. 10.52
    • D. 10.22

15. Q15. 100 mL of 2.0 × 10⁻³ M Pb(NO₃)₂ is mixed with 100 mL of 2.0 × 10⁻³ M NaI. Given Ksp(PbI₂) = 7.1 × 10⁻⁹, what happens?

    • A. No precipitate forms because Q = 1.0 × 10⁻⁹ < Ksp
    • B. A precipitate forms because Q = 1.0 × 10⁻⁹ > Ksp
    • C. A precipitate forms because Q = 4.0 × 10⁻⁹ > Ksp
    • D. No precipitate forms because Q = 8.0 × 10⁻⁹ < Ksp

16. Q16. What is the molar solubility of AgCl (Ksp = 1.8 × 10⁻¹⁰) in 0.010 M NaCl solution, neglecting the chloride from AgCl itself?

    • A. 1.8 × 10⁻¹² M
    • B. 1.3 × 10⁻⁵ M
    • C. 1.8 × 10⁻⁸ M
    • D. 1.8 × 10⁻⁵ M

17. Q17. N₂(g) + 3H₂(g) ⇌ 2NH₃(g) is at equilibrium in a rigid sealed vessel. Argon is added so that the total pressure rises but the volume is unchanged. What happens to the equilibrium position?

    • A. It shifts to the right because the volume per mole is reduced
    • B. It shifts to the left because argon displaces reactants
    • C. It shifts to the right because total pressure increased
    • D. No change, because the partial pressures of the reactants are unchanged

18. Q18. Aluminium (M = 27 g mol⁻¹) has a face-centred cubic structure and a density of 2.70 g cm⁻³ (Nₐ = 6.022 × 10²³ mol⁻¹). What is the edge length of its unit cell?

    • A. 405 pm
    • B. 286 pm
    • C. 572 pm
    • D. 320 pm

19. Q19. X-rays of wavelength 0.150 nm give a second-order (n = 2) reflection at a glancing angle of 30°. Using nλ = 2d sin θ, what is the spacing between the lattice planes?

    • A. 0.30 nm
    • B. 0.60 nm
    • C. 0.075 nm
    • D. 0.15 nm

20. Q20. The triple point of CO₂ lies at 5.2 atm and −56.6 °C. Which statement about solid CO₂ at atmospheric pressure (1 atm) is correct?

    • A. It sublimes directly to gas because 1 atm is below the triple-point pressure
    • B. It melts to liquid CO₂ because the temperature is above −56.6 °C
    • C. It melts only when the pressure is first lowered below 1 atm
    • D. It forms liquid first because 1 atm is below the critical pressure

21. Q21. For NaCl, the lattice enthalpy (energy to separate one mole of solid into gaseous ions) is +788 kJ mol⁻¹ and the total hydration enthalpy of its ions is −784 kJ mol⁻¹. What is the enthalpy of solution?

    • A. +4 kJ mol⁻¹
    • B. −1572 kJ mol⁻¹
    • C. +1572 kJ mol⁻¹
    • D. −4 kJ mol⁻¹

22. Q22. For which reaction is the entropy change of the system expected to be most negative?

    • A. N₂(g) + 3H₂(g) → 2NH₃(g)
    • B. NH₄Cl(s) → NH₃(g) + HCl(g)
    • C. 2H₂O₂(l) → 2H₂O(l) + O₂(g)
    • D. CaCO₃(s) → CaO(s) + CO₂(g)

23. Q23. How much heat is needed to convert 36 g of ice at 0 °C to water at 25 °C? (ΔH fusion = 6.01 kJ mol⁻¹; c of water = 4.18 J g⁻¹ K⁻¹; H₂O = 18)

    • A. 12.02 kJ
    • B. 15.78 kJ
    • C. 19.54 kJ
    • D. 3.76 kJ

24. Q24. At a given temperature, A ⇌ B has K = 4 and B ⇌ C has K = 0.5. What is K for 2A ⇌ 2C?

    • A. 8
    • B. 4
    • C. 2
    • D. 16

25. Q25. For A + B ⇌ C + D, K = 10. A reaction mixture has [A] = [B] = 1.0 M and [C] = [D] = 2.0 M. In which direction will the net reaction proceed?

    • A. Forward, because Q = 4 is less than K
    • B. Forward, because Q = 4 is greater than K
    • C. Backward, because Q = 0.25 is less than K
    • D. Backward, because Q = 4 is less than K

26. Q26. A gas expands from 2.0 dm³ to 5.0 dm³ against a constant external pressure of 1.0 atm. Taking 1 dm³ atm = 101.3 J, what is the work done on the gas?

    • A. +304 J
    • B. −304 J
    • C. −101 J
    • D. −507 J

27. Q27. A fixed mass of gas at constant pressure occupies 2.0 dm³ at 27 °C. At what Celsius temperature will its volume be 3.0 dm³?

    • A. 40.5 °C
    • B. 177 °C
    • C. 81 °C
    • D. 450 °C

28. Q28. At very high pressures, real gases show a compressibility factor Z = PV/nRT greater than 1. What is the main reason?

    • A. The finite volume of the molecules makes the gas harder to compress
    • B. The gas behaves as if the temperature is lower
    • C. The molecules move more slowly at high pressure
    • D. Strong attractive forces make the gas more compressible

29. Q29. 0.50 g of a volatile liquid vaporises completely to occupy 250 cm³ at 27 °C and 1.00 atm. What is its approximate molar mass? (R = 0.0821 dm³ atm K⁻¹ mol⁻¹)

    • A. 49 g mol⁻¹
    • B. 25 g mol⁻¹
    • C. 12 g mol⁻¹
    • D. 98 g mol⁻¹

30. Q30. Which pair correctly relates intermolecular forces to vapour pressure and boiling point at the same temperature?

    • A. Stronger forces give higher vapour pressure and higher boiling point
    • B. Stronger forces give lower vapour pressure and higher boiling point
    • C. Stronger forces give lower vapour pressure and lower boiling point
    • D. Stronger forces give higher vapour pressure and lower boiling point