NUMS — Medical & Dental Entry Test

NUMS Chemistry — States of Matter, Energetics and Equilibria (Set 1)

Take the NUMS Chemistry — States of Matter, Energetics and Equilibria (Set 1): 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. A hospital oxygen cylinder holds gas in 10 L at 150 atm. If the temperature stays constant, what volume would this oxygen occupy at 1 atm?
- A. 1500 L ✓
- B. 150 L
- C. 0.067 L
- D. 15 L
Answer: A. 1500 L
Explanation: Boyle's law: P₁V₁ = P₂V₂, so V₂ = 150 × 10/1 = 1500 L.
Q2. A balloon contains 2.0 L of gas at 27 °C. At constant pressure it is warmed to 177 °C. What is its new volume?
- A. 13.1 L
- B. 3.0 L ✓
- C. 1.33 L
- D. 2.5 L
Answer: B. 3.0 L
Explanation: Charles's law uses kelvin: V₂ = 2.0 × 450/300 = 3.0 L.
Q3. How many moles of an ideal gas occupy 24.6 L at 1.0 atm and 300 K? (R = 0.0821 L atm K⁻¹ mol⁻¹)
- A. 2.0 mol
- B. 1.0 mol ✓
- C. 0.1 mol
- D. 0.5 mol
Answer: B. 1.0 mol
Explanation: n = PV/RT = (1.0 × 24.6)/(0.0821 × 300) = 24.6/24.63 ≈ 1.0 mol.
Q4. Under identical conditions, what is the ratio of the rate of effusion of hydrogen (H₂) to that of oxygen (O₂)?
- A. 4 : 1 ✓
- B. 1 : 4
- C. 16 : 1
- D. 2 : 1
Answer: A. 4 : 1
Explanation: Graham's law: rate ∝ 1/√M, so rate(H₂)/rate(O₂) = √(32/2) = √16 = 4.
Q5. At a high-altitude town the atmospheric pressure is 500 torr. Air contains 21% oxygen by moles. What is the partial pressure of oxygen a climber breathes there?
- A. 160 torr
- B. 21 torr
- C. 395 torr
- D. 105 torr ✓
Answer: D. 105 torr
Explanation: Dalton's law: p(O₂) = mole fraction × total pressure = 0.21 × 500 = 105 torr. The low value explains altitude hypoxia.

The other 25 questions

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Q6. Helium and oxygen are kept at the same temperature. How do the average translational kinetic energies of their molecules compare?
- A. Oxygen's is 8 times greater
- B. Helium's is √8 times greater
- C. Helium's is 8 times greater
- D. They are equal
Q7. Anaesthetic gases stored in cylinders behave least like an ideal gas when the cylinder is in which state?
- A. Highly compressed and cold
- B. At low pressure and cold
- C. Warm and moderately compressed
- D. At low pressure and warm
Q8. In the van der Waals equation (P + an²/V²)(V − nb) = nRT, what does the constant 'a' account for?
- A. Collisions with the container walls
- B. The speed of gas molecules
- C. The actual volume of gas molecules
- D. Attractive forces between gas molecules
Q9. Food takes longer to cook in an open pot in the northern mountains than at sea level. Why?
- A. The boiling point of water rises at high altitude
- B. Air at altitude contains less oxygen for the flame
- C. Water absorbs more heat at high altitude
- D. Lower air pressure lowers the boiling point of water
Q10. Sweating cools the body. At the molecular level, why does evaporation cause cooling?
- A. Water molecules gain potential energy from the skin's surface tension
- B. Evaporation releases heat to the surroundings
- C. The fastest-moving molecules escape, lowering the average kinetic energy of those left
- D. Evaporating molecules form hydrogen bonds with air
Q11. In the crystal lattice of sodium chloride, how many Cl⁻ ions immediately surround each Na⁺ ion?
- A. 8
- B. 6
- C. 4
- D. 12
Q12. Ice floats on water, which allows aquatic life to survive winter. What is the reason ice is less dense than liquid water?
- A. Ice contains trapped air bubbles in all cases
- B. Hydrogen bonds hold molecules in an open hexagonal network in ice
- C. Water molecules in ice have more kinetic energy
- D. Covalent bonds in ice are longer than in water
Q13. For a reversible reaction, the reaction quotient Q is found to be smaller than the equilibrium constant K. What will happen?
- A. The reaction proceeds in the reverse direction
- B. The reaction proceeds in the forward direction
- C. The system is already at equilibrium
- D. The value of K decreases until it equals Q
Q14. Which statement about an exothermic reaction is correct?
- A. ΔH is positive and heat is absorbed from the surroundings
- B. ΔH is negative and the products have higher enthalpy than the reactants
- C. ΔH is negative and the products have lower enthalpy than the reactants
- D. ΔH is zero because energy is conserved
Q15. Given: C + O₂ → CO₂, ΔH = −394 kJ mol⁻¹ and CO + ½O₂ → CO₂, ΔH = −283 kJ mol⁻¹. What is ΔH for C + ½O₂ → CO?
- A. +111 kJ mol⁻¹
- B. −677 kJ mol⁻¹
- C. −283 kJ mol⁻¹
- D. −111 kJ mol⁻¹
Q16. The enthalpy of combustion of glucose is −2808 kJ mol⁻¹. How much energy is released when the body completely oxidises 9.0 g of glucose (M = 180)?
- A. 70.2 kJ
- B. 140.4 kJ
- C. 312 kJ
- D. 280.8 kJ
Q17. In a coffee-cup calorimeter, a reaction raises the temperature of 200 g of water from 25 °C to 35 °C. How much heat was released? (c = 4.18 J g⁻¹ K⁻¹)
- A. 0.836 kJ
- B. 8.36 kJ
- C. 83.6 kJ
- D. 29.3 kJ
Q18. What is the standard enthalpy of formation of O₂(g) at 298 K?
- A. −393.5 kJ mol⁻¹
- B. −286 kJ mol⁻¹
- C. Zero
- D. +142 kJ mol⁻¹
Q19. The enthalpy of neutralisation of HCl by NaOH is −57.3 kJ mol⁻¹, but for ethanoic acid with NaOH it is less negative. Why?
- A. Ethanoic acid is a stronger acid than HCl
- B. Ethanoic acid gives two H⁺ ions per molecule
- C. Some energy is used to ionise the weak ethanoic acid
- D. Water is not formed in the second reaction
Q20. Why is the lattice energy of MgO much greater than that of NaCl?
- A. MgO is a covalent compound
- B. Mg²⁺ and O²⁻ carry higher charges and are smaller ions
- C. Na⁺ and Cl⁻ have higher charges
- D. MgO has weaker electrostatic attractions
Q21. Using the bond enthalpies H–H = 436, Cl–Cl = 243 and H–Cl = 432 kJ mol⁻¹, what is ΔH for H₂ + Cl₂ → 2HCl?
- A. −247 kJ mol⁻¹
- B. +247 kJ mol⁻¹
- C. −185 kJ mol⁻¹
- D. +185 kJ mol⁻¹
Q22. What is the correct equilibrium constant expression (Kc) for N₂(g) + 3H₂(g) ⇌ 2NH₃(g)?
- A. [NH₃]² / ([N₂][H₂]³)
- B. [N₂][H₂]³ / [NH₃]²
- C. 2[NH₃] / ([N₂] × 3[H₂])
- D. [NH₃] / ([N₂][H₂])
Q23. For N₂(g) + 3H₂(g) ⇌ 2NH₃(g), what is the effect of increasing the total pressure at constant temperature?
- A. Equilibrium shifts to the right, increasing the yield of NH₃
- B. The value of Kc increases
- C. Equilibrium shifts to the left, decreasing NH₃
- D. No change, because K is constant
Q24. Oxygen binds to haemoglobin reversibly: Hb + O₂ ⇌ HbO₂. Why does haemoglobin release oxygen in active muscle tissue?
- A. The high O₂ concentration there shifts the equilibrium to the right
- B. The equilibrium constant becomes zero in muscle
- C. The low O₂ concentration there shifts the equilibrium to the left
- D. Haemoglobin is destroyed in muscle tissue
Q25. For H₂(g) + I₂(g) ⇌ 2HI(g), the equilibrium concentrations are [H₂] = 0.2 M, [I₂] = 0.2 M and [HI] = 1.6 M. What is Kc?
- A. 8
- B. 64
- C. 0.016
- D. 40
Q26. For which of the following gas-phase equilibria do Kp and Kc have the same numerical value at any temperature?
- A. N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
- B. H₂(g) + Cl₂(g) ⇌ 2HCl(g)
- C. 2SO₂(g) + O₂(g) ⇌ 2SO₃(g)
- D. PCl₅(g) ⇌ PCl₃(g) + Cl₂(g)
Q27. What effect does adding a catalyst have on a system at equilibrium?
- A. Equilibrium shifts towards the reactants
- B. Equilibrium shifts towards the products
- C. The equilibrium constant increases
- D. Equilibrium is reached faster but its position is unchanged
Q28. Barium sulphate is given as a 'barium meal' for X-ray imaging because it is very insoluble. If Ksp(BaSO₄) = 1.0 × 10⁻¹⁰ at body temperature, what is its molar solubility?
- A. 1.0 × 10⁻¹⁰ mol dm⁻³
- B. 1.0 × 10⁻²⁰ mol dm⁻³
- C. 5.0 × 10⁻¹¹ mol dm⁻³
- D. 1.0 × 10⁻⁵ mol dm⁻³
Q29. How does the solubility of AgCl in a 0.1 M NaCl solution compare with its solubility in pure water?
- A. It is higher because of the extra ions
- B. It is the same because Ksp is constant
- C. It is lower because of the common ion effect
- D. It is higher because Na⁺ complexes Ag⁺
Q30. For an exothermic equilibrium reaction, what happens when the temperature is raised?
- A. K decreases and the equilibrium shifts towards the reactants
- B. K stays the same but the rate decreases
- C. K decreases and the equilibrium shifts towards the products
- D. K increases and the equilibrium shifts towards the products