NUMS — Medical & Dental Entry Test

NUMS Chemistry — States of Matter, Energetics and Equilibria (Set 3)

Take the NUMS Chemistry — States of Matter, Energetics and Equilibria (Set 3): 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. What is the density of carbon dioxide gas at STP? (C = 12, O = 16; molar volume at STP = 22.4 L/mol)
- A. 0.98 g/L
- B. 2.24 g/L
- C. 1.96 g/L ✓
- D. 0.51 g/L
Answer: C. 1.96 g/L
Explanation: Density = M/Vm = 44/22.4 = 1.96 g/L.
Q2. A gas X takes 40 s to effuse through a small hole while the same volume of oxygen (M = 32) takes 20 s under identical conditions. What is the molar mass of X?
- A. 16 g/mol
- B. 64 g/mol
- C. 256 g/mol
- D. 128 g/mol ✓
Answer: D. 128 g/mol
Explanation: Rate ∝ 1/time. t_X/t_O₂ = √(M_X/M_O₂), so 2 = √(M_X/32) and M_X = 4 × 32 = 128 g/mol.
Q3. A mixture contains 4 g of helium and 16 g of oxygen (He = 4, O = 16) at a total pressure of 6 atm. What is the partial pressure of helium?
- A. 2 atm
- B. 1 atm
- C. 4 atm ✓
- D. 3 atm
Answer: C. 4 atm
Explanation: Moles: He = 1.0, O₂ = 0.5; mole fraction of He = 1/1.5 = 2/3, so p = 6 × 2/3 = 4 atm.
Q4. What volume is occupied by 0.50 mole of an ideal gas at 27 °C and 2.0 atm? (R = 0.0821 L atm K⁻¹ mol⁻¹)
- A. 6.16 L ✓
- B. 12.32 L
- C. 0.55 L
- D. 24.63 L
Answer: A. 6.16 L
Explanation: V = nRT/P = 0.50 × 0.0821 × 300/2.0 = 6.16 L.
Q5. A sealed rigid cylinder contains gas at 1.0 atm and 27 °C. If it is heated to 127 °C, what will be the pressure?
- A. 0.75 atm
- B. 2.0 atm
- C. 4.7 atm
- D. 1.33 atm ✓
Answer: D. 1.33 atm
Explanation: At constant volume P₁/T₁ = P₂/T₂: P₂ = 1.0 × 400/300 = 1.33 atm (temperature must be in kelvin).

The other 25 questions

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Q6. Under which conditions do real gases show the greatest deviation from ideal behaviour?
- A. High pressure and high temperature
- B. Low pressure and low temperature
- C. Low pressure and high temperature
- D. High pressure and low temperature
Q7. Which of the gases He, H₂, N₂ and NH₃ has the largest van der Waals constant 'a' (a measure of intermolecular attraction)?
- A. H₂
- B. He
- C. N₂
- D. NH₃
Q8. What does the critical temperature of a gas represent?
- A. The temperature at which the gas liquefies at 1 atm
- B. The temperature at which vapour pressure equals 760 torr
- C. The temperature above which the gas cannot be liquefied by pressure alone
- D. The temperature at which all molecular motion ceases
Q9. Water rises in a narrow glass capillary tube because of which of the following?
- A. Atmospheric pressure is higher inside the tube
- B. Cohesion within water is stronger than adhesion to glass
- C. Adhesion between water and glass is stronger than cohesion within water
- D. Water has a lower density than glass
Q10. Why does water boil at a lower temperature at the top of a high mountain?
- A. The heat of vaporisation of water becomes zero at height
- B. Atmospheric pressure is lower, so vapour pressure reaches it sooner
- C. Oxygen concentration is lower, so heating is less effective
- D. Water molecules have weaker bonds at high altitude
Q11. How many atoms belong to one body-centred cubic (BCC) unit cell?
- A. 1
- B. 4
- C. 6
- D. 2
Q12. At the same temperature, which liquid has the highest vapour pressure?
- A. Ethanol
- B. Water
- C. Glycerol
- D. Diethyl ether
Q13. Why does ice float on liquid water?
- A. Hydrogen bonding holds ice molecules in an open, less dense lattice
- B. Surface tension supports the ice on the water
- C. Ice molecules are lighter than liquid water molecules
- D. Ice contains many trapped air bubbles
Q14. How much heat is required to raise the temperature of 250 g of water from 20 °C to 60 °C? (specific heat = 4.18 J g⁻¹ °C⁻¹)
- A. 10.4 kJ
- B. 62.7 kJ
- C. 41.8 kJ
- D. 418 kJ
Q15. The enthalpy of vaporisation of water is 40.7 kJ mol⁻¹. How much heat is needed to vaporise 36 g of water at its boiling point? (H₂O = 18 g/mol)
- A. 81.4 kJ
- B. 20.4 kJ
- C. 40.7 kJ
- D. 162.8 kJ
Q16. Estimate ΔH for H₂ + Cl₂ → 2HCl using bond enthalpies H–H = 436, Cl–Cl = 243 and H–Cl = 431 kJ mol⁻¹.
- A. -183 kJ
- B. +183 kJ
- C. −862 kJ
- D. +679 kJ
Q17. For N₂(g) + 3H₂(g) → 2NH₃(g), ΔH = −92 kJ at 300 K. What is ΔU? (R = 8.314 J K⁻¹ mol⁻¹)
- A. -87.0 kJ
- B. -82.0 kJ
- C. -97.0 kJ
- D. −92.0 kJ
Q18. For which of the following changes is the entropy change negative?
- A. Evaporation of ethanol
- B. 2NO₂(g) → N₂O₄(g)
- C. Dissolving of KNO₃ in water
- D. Melting of ice
Q19. A reaction has ΔH = +40 kJ mol⁻¹ and ΔS = +120 J K⁻¹ mol⁻¹. Above what temperature does it become spontaneous?
- A. 33 K
- B. 120 K
- C. 333 K
- D. 480 K
Q20. The enthalpy of combustion of C(s) to CO₂(g) is −393.5 kJ mol⁻¹ and that of CO(g) to CO₂(g) is −283.0 kJ mol⁻¹. What is the enthalpy of formation of CO(g)?
- A. −283.0 kJ mol⁻¹
- B. −676.5 kJ mol⁻¹
- C. +110.5 kJ mol⁻¹
- D. −110.5 kJ mol⁻¹
Q21. For N₂O₄(g) ⇌ 2NO₂(g), the equilibrium concentrations are [N₂O₄] = 0.20 M and [NO₂] = 0.40 M. What is Kc?
- A. 0.80 mol dm⁻³
- B. 2.0 mol dm⁻³
- C. 1.6 mol dm⁻³
- D. 0.50 mol dm⁻³
Q22. 1.0 mol of H₂ and 1.0 mol of I₂ are placed in a 1.0 dm³ vessel. At equilibrium 1.2 mol of HI is present. What is Kc for H₂ + I₂ ⇌ 2HI?
- A. 3.0
- B. 2.25
- C. 1.5
- D. 9.0
Q23. 1.0 mol of PCl₅ in a 1.0 dm³ vessel dissociates 40% according to PCl₅ ⇌ PCl₃ + Cl₂. What is Kc?
- A. 0.67 mol dm⁻³
- B. 0.27 mol dm⁻³
- C. 0.40 mol dm⁻³
- D. 0.16 mol dm⁻³
Q24. For a reaction at a certain temperature, K = 5.0 and the reaction quotient Q = 2.0. In which direction will the reaction proceed?
- A. It cannot be predicted without the rate constants
- B. Forward, to form more products
- C. Backward, to form more reactants
- D. It is already at equilibrium
Q25. What is the relationship between Kp and Kc for the synthesis of ammonia, N₂(g) + 3H₂(g) ⇌ 2NH₃(g)?
- A. Kp = Kc(RT)⁻²
- B. Kp = Kc
- C. Kp = Kc(RT)²
- D. Kp = Kc(RT)⁻⁴
Q26. The solubility product of AgCl is 1.8 × 10⁻¹⁰ mol² dm⁻⁶. What is its molar solubility in pure water?
- A. 9.0 × 10⁻¹¹ mol dm⁻³
- B. 1.8 × 10⁻¹⁰ mol dm⁻³
- C. 1.34 × 10⁻⁵ mol dm⁻³
- D. 3.6 × 10⁻¹⁰ mol dm⁻³
Q27. Equal volumes of 2.0 × 10⁻⁵ M AgNO₃ and 2.0 × 10⁻⁵ M NaCl are mixed. Will AgCl (Ksp = 1.8 × 10⁻¹⁰) precipitate?
- A. No, because AgCl is soluble in water
- B. No, because the ionic product 1.0 × 10⁻¹⁰ is less than Ksp
- C. Yes, because the ionic product 4.0 × 10⁻¹⁰ exceeds Ksp
- D. Yes, because both ions are present
Q28. For 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) at equilibrium in a rigid vessel, an inert gas such as argon is added at constant volume. What happens to the position of equilibrium?
- A. It shifts right because the total pressure increases
- B. No shift, because the partial pressures of the reacting gases are unchanged
- C. It shifts left because the total pressure increases
- D. It shifts right because the volume decreases
Q29. The Haber process for ammonia (exothermic) is run at about 450 °C even though a lower temperature would favour a higher equilibrium yield. Why?
- A. Ammonia is unstable below 450 °C
- B. The catalyst works only above 450 °C because it melts
- C. A moderate temperature gives an acceptable rate while keeping a reasonable yield
- D. Higher temperature increases the equilibrium constant
Q30. What happens to the equilibrium constant of an exothermic reaction when the temperature is raised?
- A. It increases
- B. It decreases
- C. It becomes zero
- D. It is unchanged