NUMS — Medical & Dental Entry Test

NUMS Chemistry — States of Matter, Energetics and Equilibria (Set 2)

Take the NUMS Chemistry — States of Matter, Energetics and Equilibria (Set 2): 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.

Q1. Ammonia leaking from a refrigeration plant rises towards the ceiling. Treating it as an ideal gas, what is its density at STP? (NH₃ = 17 g mol⁻¹, molar volume = 22.4 dm³)
- A. 1.29 g dm⁻³
- B. 0.76 g dm⁻³ ✓
- C. 0.38 g dm⁻³
- D. 1.32 g dm⁻³
Answer: B. 0.76 g dm⁻³
Explanation: Density = M/Vₘ = 17/22.4 = 0.76 g dm⁻³, lower than air (about 1.29 g dm⁻³), so ammonia rises.
Q2. A sample of gas occupies 500 cm³ at 27 °C and 1 atm. What volume will it occupy at 127 °C and 2 atm?
- A. 1333 cm³
- B. 333 cm³ ✓
- C. 750 cm³
- D. 1176 cm³
Answer: B. 333 cm³
Explanation: V₂ = V₁ × (P₁/P₂) × (T₂/T₁) = 500 × (1/2) × (400/300) = 333 cm³ (temperatures must be in kelvin).
Q3. 0.50 g of an unknown gas occupies 0.41 dm³ at 1.0 atm and 300 K. What is its molar mass? (R = 0.0821 dm³ atm K⁻¹ mol⁻¹)
- A. 15 g mol⁻¹
- B. 60 g mol⁻¹
- C. 30 g mol⁻¹ ✓
- D. 45 g mol⁻¹
Answer: C. 30 g mol⁻¹
Explanation: n = PV/RT = (1.0 × 0.41)/(0.0821 × 300) = 0.0166 mol; M = 0.50/0.0166 = 30 g mol⁻¹.
Q4. A gas effuses through a pinhole at exactly half the rate of methane (CH₄, M = 16) under the same conditions. What is the molar mass of the gas?
- A. 8 g mol⁻¹
- B. 32 g mol⁻¹
- C. 64 g mol⁻¹ ✓
- D. 4 g mol⁻¹
Answer: C. 64 g mol⁻¹
Explanation: By Graham's law r₁/r₂ = √(M₂/M₁): 1/2 = √(16/M), so M = 16 × 4 = 64 g mol⁻¹ (e.g. SO₂).
Q5. If Charles's law held exactly down to the lowest temperatures, at what temperature would the volume of an ideal gas become zero?
- A. 0 °C
- B. −273.15 °C ✓
- C. −100 °C
- D. −373.15 °C
Answer: B. −273.15 °C
Explanation: Extrapolating V–T lines to zero volume gives −273.15 °C, the absolute zero (0 K).

The other 25 questions

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Q6. A cylinder contains 2 mol of nitrogen and 3 mol of oxygen at a total pressure of 10 atm. What is the partial pressure of oxygen?
- A. 3 atm
- B. 4 atm
- C. 10 atm
- D. 6 atm
Q7. The compressibility factor Z = PV/nRT of hydrogen gas is greater than 1 at very high pressure. What is the main reason?
- A. Hydrogen molecules dissociate into atoms
- B. Attractive forces between H₂ molecules become very strong
- C. The finite volume of the gas molecules becomes significant
- D. The gas behaves exactly as an ideal gas
Q8. Glycerol (propane-1,2,3-triol) is far more viscous than water at room temperature. What is the main reason?
- A. Each glycerol molecule has three –OH groups, forming extensive hydrogen bonding
- B. Glycerol molecules are non-polar
- C. Glycerol is an ionic compound
- D. Glycerol has a lower molar mass than water
Q9. Which of these liquids has the highest vapour pressure at 25 °C?
- A. Water
- B. Ethanol
- C. Glycerol
- D. Diethyl ether
Q10. How many atoms belong to one unit cell of a face-centred cubic (fcc) lattice?
- A. 8
- B. 2
- C. 1
- D. 4
Q11. Window glass softens gradually over a range of temperatures instead of melting sharply. This is because glass is:
- A. an amorphous solid with no long-range order
- B. a crystalline ionic solid
- C. a molecular crystal of SiO₂ units
- D. a metallic solid
Q12. Graphite conducts electricity but diamond does not, although both are pure carbon. Why?
- A. In graphite each carbon is sp² hybridised, leaving one delocalised electron per atom
- B. Diamond's carbon atoms are sp² hybridised
- C. Graphite has free carbon ions
- D. Diamond contains ionic bonds that trap electrons
Q13. Iodine forms soft crystals that sublime on gentle warming. What type of crystalline solid is iodine?
- A. Metallic solid
- B. Covalent network solid
- C. Ionic solid
- D. Molecular solid held by London dispersion forces
Q14. Instant cold packs used for sports injuries contain ammonium nitrate, which dissolves in water and the pack becomes cold. Which statement is correct?
- A. The process is endothermic and ΔH is positive
- B. The process is endothermic and ΔH is negative
- C. The process is exothermic and ΔH is negative
- D. No energy change takes place
Q15. Use these enthalpies of combustion to find the enthalpy of formation of ethane, 2C(s) + 3H₂(g) → C₂H₆(g): carbon −394, hydrogen −286, ethane −1560 kJ mol⁻¹.
- A. −86 kJ mol⁻¹
- B. −3206 kJ mol⁻¹
- C. −880 kJ mol⁻¹
- D. +86 kJ mol⁻¹
Q16. When 0.050 mol of an acid is neutralised in a calorimeter, the temperature of 100 g of solution rises by 6.0 °C. What is the enthalpy change per mole of acid? (c = 4.18 J g⁻¹ K⁻¹)
- A. −125 kJ mol⁻¹
- B. −2.51 kJ mol⁻¹
- C. +50.2 kJ mol⁻¹
- D. −50.2 kJ mol⁻¹
Q17. The enthalpy of atomisation of methane, CH₄(g) → C(g) + 4H(g), is +1664 kJ mol⁻¹. What is the average C–H bond enthalpy?
- A. 1664 kJ mol⁻¹
- B. 333 kJ mol⁻¹
- C. 832 kJ mol⁻¹
- D. 416 kJ mol⁻¹
Q18. Standard enthalpy changes are quoted under standard conditions. Which set describes these conditions?
- A. 373 K, 1 atm pressure and pure liquids only
- B. 298 K, 1 atm pressure and 1 mol dm⁻³ solutions
- C. 273 K, 1 atm pressure and 1 mol dm⁻³ solutions
- D. 298 K, 2 atm pressure and 0.1 mol dm⁻³ solutions
Q19. For a salt MX, the lattice dissociation enthalpy is +788 kJ mol⁻¹ and the total hydration enthalpy of its ions is −784 kJ mol⁻¹. What is its enthalpy of solution?
- A. −4 kJ mol⁻¹
- B. +1572 kJ mol⁻¹
- C. +4 kJ mol⁻¹
- D. −1572 kJ mol⁻¹
Q20. In the Born–Haber cycle for sodium chloride, which step is exothermic?
- A. Gaining an electron by a gaseous chlorine atom (first electron affinity)
- B. Atomisation of solid sodium
- C. Ionisation of a gaseous sodium atom
- D. Breaking the Cl–Cl bond
Q21. 1.0 mol of PCl₅ is heated in a 1.0 dm³ vessel and 40% of it dissociates: PCl₅ ⇌ PCl₃ + Cl₂. What is Kc at this temperature?
- A. 0.16 mol dm⁻³
- B. 1.07 mol dm⁻³
- C. 0.67 mol dm⁻³
- D. 0.27 mol dm⁻³
Q22. What are the units of Kc for the equilibrium N₂O₄(g) ⇌ 2NO₂(g)?
- A. mol² dm⁻⁶
- B. No units
- C. mol dm⁻³
- D. mol⁻¹ dm³
Q23. For the Haber equilibrium N₂(g) + 3H₂(g) ⇌ 2NH₃(g), which relation between Kp and Kc is correct?
- A. Kp = Kc(RT)⁴
- B. Kp = Kc
- C. Kp = Kc(RT)⁻²
- D. Kp = Kc(RT)²
Q24. Argon is pumped into a sealed, rigid vessel containing the equilibrium 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), keeping the volume and temperature constant. What happens to the equilibrium?
- A. Kc increases
- B. It does not shift, because the partial pressures of the reacting gases are unchanged
- C. It shifts to the left because argon reacts with SO₃
- D. It shifts to the right because total pressure increases
Q25. Low temperature favours a higher equilibrium yield of ammonia in the Haber process, yet plants operate at about 450 °C. Why?
- A. The iron catalyst works only above 1000 °C
- B. The reaction is endothermic
- C. Ammonia decomposes completely below 400 °C
- D. At low temperature the rate is too slow, so 450 °C is a compromise between rate and yield
Q26. For the reaction A ⇌ B, K = 4 at a certain temperature. What is the equilibrium constant for 2B ⇌ 2A at the same temperature?
- A. 1/4
- B. 1/16
- C. 1/8
- D. 16
Q27. The solubility of calcium fluoride, CaF₂, in water is 2.0 × 10⁻⁴ mol dm⁻³ at a certain temperature. What is its solubility product Ksp?
- A. 8.0 × 10⁻¹²
- B. 3.2 × 10⁻¹¹
- C. 4.0 × 10⁻⁸
- D. 1.6 × 10⁻¹¹
Q28. Two solutions are mixed and the ionic product of a sparingly soluble salt exceeds its Ksp. What will be observed?
- A. A precipitate forms until the ionic product falls to Ksp
- B. The salt dissolves further
- C. Nothing happens because the solution is unsaturated
- D. Ksp increases to match the ionic product
Q29. Which statement about a system at chemical equilibrium is correct?
- A. The forward and reverse reaction rates are equal and concentrations stay constant
- B. The concentrations of reactants and products must be equal
- C. Only the forward reaction continues
- D. Both reactions have stopped completely
Q30. For a reaction at 298 K, Kc = 1 × 10³⁰. What does this very large value indicate?
- A. At equilibrium the mixture consists almost entirely of products
- B. At equilibrium the mixture consists almost entirely of reactants
- C. The reaction needs a catalyst to occur
- D. The reaction is extremely fast