9th class Chemistry, Chapter 5: Energetics MCQs

1. The reaction H₂ + Cl₂ --(sunlight)--> 2HCl is an exothermic reaction. From where does the energy come to break the bonds of H₂ and Cl₂?

1. (A) By collisions between the molecules
2. (B) From sunlight ✓
3. (C) From the surrounding
4. (D) By collisions of the molecules with the walls of the container

2. Which of the following reactions has the least value of activation energy?

1. (A) H₂(g) + ½O₂(g) → H₂O(g)
2. (B) C(s) + O₂(g) → CO₂(g)
3. (C) NaCl(aq) + AgNO₃(aq) → AgCl(s) + NaNO₃(aq) ✓
4. (D) H₂(g) + I₂(s) → 2HI(g)

3. Formation of which hydrogen halide from the elements is an endothermic reaction?

1. (A) HCl
2. (B) HF
3. (C) HBr
4. (D) HI ✓

4. What are the products of anaerobic respiration?

1. (A) ATP + CO₂ + H₂O
2. (B) CO₂ + H₂O
3. (C) ATP + Ethanol + H₂O ✓
4. (D) Ethanol + H₂O

5. Which reaction do you expect to be a reversible reaction? (energy profiles of A + B → C + D)

1. (A) Products C + D much lower in energy than reactants A + B
2. (B) Products C + D at the same energy as reactants A + B ✓
3. (C) Products C + D a little higher in energy than reactants A + B
4. (D) Products C + D much higher, close to the top of the curve

6. What does it show when a chemical reaction is exothermic?

1. (A) It shows the bonds which break are weaker than those are formed. ✓
2. (B) It shows the bond which break are stronger than those are formed.
3. (C) Exothermic nature of the reaction is not concerned with bond formation or bond breakage.
4. (D) It shows that the reactants are more stable than the products.

7. When NaOH and HCl are mixed the temperature increases. The reaction is:

1. (A) endothermic with a positive enthalpy change.
2. (B) endothermic with a negative enthalpy change.
3. (C) exothermic with a positive enthalpy change.
4. (D) exothermic with a negative enthalpy change. ✓

8. The average bond dissociation energy for the C−H bond is 412 kJ mol⁻¹. Which of the following process will have enthalpy change close to 412 kJ mol⁻¹?

1. (A) CH₄(g) → C(g) + 2H₂(g)
2. (B) CH₄(g) → C(s) + 2H₂(g)
3. (C) CH₄(g) → C(g) + 4H(g)
4. (D) CH₄(g) → CH₃(g) + H(g) ✓

9. The average bond energies for O−O and O=O are 146 and 496 kJ mol⁻¹ respectively. Find the enthalpy in kJ for the reaction H−O−O−H(g) → H−O−H(g) + ½O=O(g)

1. (A) −102 kJ ✓
2. (B) +102 kJ
3. (C) +350 kJ
4. (D) +394 kJ

10. Why does the following exothermic reaction not occur? C(Diamond) → C(Graphite), ΔH = −3 kJ mol⁻¹

1. (A) Structure of diamond is more stable than that of graphite.
2. (B) Diamond has strong covalent bonds than does the graphite.
3. (C) The change from diamond to graphite has high activation energy. ✓
4. (D) Density of graphite is less than that of diamond.

11. Energy that is stored in a molecule in which atoms are bonded to each other is:

1. (A) Light energy
2. (B) Chemical energy ✓
3. (C) Heat energy
4. (D) Kinetic energy

12. The unit of enthalpy is:

1. (A) amu
2. (B) kJ mol⁻¹ ✓
3. (C) g mol⁻¹
4. (D) mol dm⁻³

13. Chemical energetics is part of a broader field called:

1. (A) Electrochemistry
2. (B) Biochemistry
3. (C) Thermodynamics ✓
4. (D) Stoichiometry

14. The word "energy" was first used in physics in 1802 by:

1. (A) Niels Bohr
2. (B) Thomas Young ✓
3. (C) John Dalton
4. (D) Avogadro

15. Any physical or chemical change under study is called a:

1. (A) System ✓
2. (B) Surrounding
3. (C) Reaction coordinate
4. (D) Transition state

16. When energy is transferred from the surrounding to the system, the change is:

1. (A) Exothermic with a negative sign
2. (B) Endothermic with a negative sign
3. (C) Exothermic with a positive sign
4. (D) Endothermic with a positive sign ✓

17. In an exothermic change the surroundings get:

1. (A) No change
2. (B) Frozen
3. (C) Warmer ✓
4. (D) Cooler

18. The standard conditions for heat content are:

1. (A) 100 °C and 760 mm pressure
2. (B) 0 °C and 100 mm pressure
3. (C) 0 °C and 760 mm pressure ✓
4. (D) 25 °C and 1 mm pressure

19. The change in enthalpy is represented by:

1. (A) ΔE₂
2. (B) ΔH ✓
3. (C) H
4. (D) Eₐ

20. For 2CO(g) + O₂(g) → 2CO₂(g), ΔH° = −566.0 kJ. The reaction is:

1. (A) Reversible only
2. (B) Exothermic ✓
3. (C) Endothermic
4. (D) Neither