ECAT — Engineering College Admission Test (UET)
Take the ECAT Chemistry — Thermochemistry, Equilibrium and Kinetics (Set 2): 30 multiple-choice questions (40 minutes) with instant scoring and a full…
What this test covers
The first 5 questions of this test, with the correct answer and explanation.
Q1. Given enthalpies of combustion (kJ mol⁻¹): C(graphite) −393.5, H₂(g) −285.8, CH₄(g) −890.3, the standard enthalpy of formation of CH₄ is:
Answer: B. −74.8 kJ mol⁻¹
Explanation: ΔHf = ΔHc(C) + 2ΔHc(H₂) − ΔHc(CH₄) = −393.5 − 571.6 + 890.3 = −74.8 kJ mol⁻¹.
Q2. 50 cm³ of 1.0 M HCl is mixed with 50 cm³ of 1.0 M NaOH and the temperature rises by 6.8°C. Taking the mass of solution as 100 g and c = 4.18 J g⁻¹ K⁻¹, the enthalpy of neutralization is about:
Answer: A. −56.8 kJ mol⁻¹
Explanation: q = 100 × 4.18 × 6.8 = 2842 J for 0.05 mol of water formed; ΔH = −2842/0.05 = −56.8 kJ mol⁻¹.
Q3. A system absorbs 50 J of heat and does 20 J of work on its surroundings. The change in its internal energy is:
Answer: D. +30 J
Explanation: First law: ΔE = q + w = (+50) + (−20) = +30 J (work done by the system is negative).
Q4. A bomb calorimeter measures the heat of reaction at constant volume. This heat is equal to:
Answer: C. ΔE
Explanation: At constant volume no pressure–volume work is done, so q(v) = ΔE; ΔH is then obtained from ΔH = ΔE + ΔnRT.
Q5. Which statement about the standard enthalpy of combustion is correct?
Answer: D. It is always negative because combustion is exothermic
Explanation: Enthalpy of combustion is the heat released when 1 mol of a substance burns completely in oxygen; heat is always given out.
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Q6. Dissolving NH₄Cl in water makes the solution cold, yet the process occurs spontaneously. This shows that:
Q7. 1.0 mol each of H₂ and I₂ are heated in a 1 dm³ flask. At equilibrium 1.6 mol of HI is present (H₂ + I₂ ⇌ 2HI). The value of Kc is:
Q8. For 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), the relation between Kp and Kc is:
Q9. For a reaction mixture, the reaction quotient Q is found to be greater than Kc. The reaction will:
Q10. For H₂(g) + I₂(g) ⇌ 2HI(g), Kc = 49 at a certain temperature. At the same temperature, Kc for ½H₂(g) + ½I₂(g) ⇌ HI(g) is:
Q11. An inert gas such as argon is added to the equilibrium N₂ + 3H₂ ⇌ 2NH₃ at constant volume. The equilibrium:
Q12. For an exothermic equilibrium, raising the temperature:
Q13. The pH of a 0.01 M NaOH solution at 25°C is:
Q14. The pH of a 1 × 10⁻⁸ M HCl solution at 25°C is closest to:
Q15. The pH of a 0.05 M H₂SO₄ solution (assume complete ionization) is:
Q16. At 50°C, Kw is greater than 1 × 10⁻¹⁴. Pure water at this temperature has:
Q17. The Ksp of AgBr is 4.9 × 10⁻¹³ at 25°C. Its solubility in pure water is:
Q18. A precipitate of a sparingly soluble salt forms when:
Q19. A buffer contains equal concentrations of NH₃ and NH₄Cl. If pKb of NH₃ is 4.74, the pH of the buffer at 25°C is:
Q20. The degree of ionization of a 0.01 M weak acid with Ka = 1 × 10⁻⁶ is about:
Q21. For 2N₂O₅ → 4NO₂ + O₂, if N₂O₅ disappears at 0.02 mol dm⁻³ s⁻¹, NO₂ is formed at:
Q22. For A + B → products: doubling [A] at constant [B] doubles the rate, and doubling [B] at constant [A] makes the rate four times larger. The overall order is:
Q23. The units of the rate constant of a second-order reaction are:
Q24. A first-order decomposition has a half-life of 15 min. Starting with 80 g of reactant, the mass left after 1 hour is:
Q25. A first-order reaction has a half-life of 5 min. About how long will it take for 99.9% of the reactant to react?
Q26. For a reaction, the activation energy of the forward reaction is 80 kJ mol⁻¹ and that of the backward reaction is 120 kJ mol⁻¹. The ΔH of the forward reaction is:
Q27. Arsenic compounds present as impurities in SO₂ reduce the activity of the platinum catalyst in the contact process. This effect is called:
Q28. The specific rate constant k of a reaction changes when:
Q29. The rate of the reaction CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH can conveniently be followed by measuring the change in:
Q30. For the equilibrium H₂(g) + I₂(g) ⇌ 2HI(g), increasing the total pressure by compressing the mixture: