A-Level H2 Chemistry 1 ā Questions and Answers
Question 1: What is the electronic configuration of a ground-state iron atom (Fe, Z=26)?
- [Ar] 3dā¶ 4sĀ² (Correct answer)
- [Ar] 3dāø
- [Ar] 4sĀ² 4pā¶
- [Ne] 3dā¶ 4sĀ²
Correct answer: [Ar] 3dā¶ 4sĀ²
Iron (Fe, Z=26): [Ar] is 1sĀ²2sĀ²2pā¶3sĀ²3pā¶ (18 electrons). Then 3dā¶4sĀ² accounts for the remaining 8. Full: [Ar] 3dā¶ 4sĀ².
Question 2: What is the enthalpy change of neutralisation and what is its typical value for a strong acidāstrong base reaction?
- ā56 kJ/mol (Correct answer)
- ā46 kJ/mol
- +56 kJ/mol
- ā100 kJ/mol
Correct answer: ā56 kJ/mol
The standard enthalpy of neutralisation for a strong acid and strong base is approximately ā57 kJ/mol (often quoted as ā56 kJ/mol), representing Hāŗ(aq) + OHā»(aq) ā HāO(l).
Question 3: Which hybridisation is exhibited by the carbon atoms in benzene?
- spĀ³
- sp
- spĀ² (Correct answer)
- spĀ³d
Correct answer: spĀ²
In benzene, each carbon is spĀ² hybridised, forming three sigma bonds (two C-C, one C-H) and contributing one electron to the delocalised Ļ system above and below the ring.
Question 4: What is the meaning of 'rate of reaction'?
- Total moles of product formed
- Change in concentration of a reactant or product per unit time (Correct answer)
- Activation energy of the reaction
- Total energy released
Correct answer: Change in concentration of a reactant or product per unit time
Rate of reaction is defined as the change in concentration of a reactant (decrease) or product (increase) per unit time, expressed in mol dmā»Ā³ sā»Ā¹.
Question 5: What is the order of reaction if doubling the concentration of A doubles the rate?
- Zero order
- First order (Correct answer)
- Second order
- Third order
Correct answer: First order
If rate ā [A]Ā¹, doubling [A] doubles the rate. This is first order with respect to A.
Question 6: In the Born-Haber cycle, which step represents the formation of gaseous ions from gaseous atoms?
- Enthalpy of atomisation
- Lattice enthalpy
- Ionisation energy (Correct answer)
- Electron affinity
Correct answer: Ionisation energy
Ionisation energy is the energy required to remove an electron from a gaseous atom to form a positive ion. Electron affinity is the energy change for adding an electron.
A-Level H2 Chemistry 1
What is the electronic configuration of a ground-state iron atom (Fe, Z=26)?