H2 Chemistry Flashcards

What is the electronic configuration of a ground-state iron atom (Fe, Z=26)?

Answer: [Ar] 3d⁶ 4s²

Iron (Fe, Z=26): [Ar] is 1s²2s²2p⁶3s²3p⁶ (18 electrons). Then 3d⁶4s² accounts for the remaining 8. Full: [Ar] 3d⁶ 4s².

What is the enthalpy change of neutralisation and what is its typical value for a strong acid–strong base reaction?

Answer: −56 kJ/mol

The standard enthalpy of neutralisation for a strong acid and strong base is approximately −57 kJ/mol (often quoted as −56 kJ/mol), representing H⁺(aq) + OH⁻(aq) → H₂O(l).

Which hybridisation is exhibited by the carbon atoms in benzene?

Answer: sp²

In benzene, each carbon is sp² hybridised, forming three sigma bonds (two C-C, one C-H) and contributing one electron to the delocalised π system above and below the ring.

What is the meaning of 'rate of reaction'?

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 dm⁻³ s⁻¹.

What is the order of reaction if doubling the concentration of A doubles the rate?

Answer: First order

If rate ∝ [A]¹, doubling [A] doubles the rate. This is first order with respect to A.

In the Born-Haber cycle, which step represents the formation of gaseous ions from gaseous atoms?

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.