Which of the following equations represents the second ionization energy of calcium?

04A

Question

Which of the following equations represents the second ionization energy of calcium?

04A

BlackTom AI · Accepted Answer

To tackle this question, I’ll examine what the second ionization energy means and then evaluate each option.

First, recall that the second ionization energy is the energy required to remove a second electron after the first has already been removed. For calcium, the first ionization removes one electron from neutral Ca to form Ca+(g); the second ionization energy would then remove another electron from Ca+(g) to yield Ca2+(g).

Option 1: Ca+(g) → Ca2+(g) + e–. This aligns precisely with the definition of the second ionization energy: removing a second electron from the singly charged ion Ca+ to form Ca2+. It is therefore the correct representation of the process.

Option 2: Ca(g) → Ca2+(g) + 2e–. This describes removing two electrons directly from neutral calcium in one step, which would correspond to the combined energy of the first and second ionizations summed, not specifically the second ionization energy. It does not match the required intermediate species (Ca+) for the second ionization.

Option 3: Ca2+(g) + e– → Ca+(g). This is the reverse of the second ionization process: it would be electron capture by Ca2+ to form Ca+. Ionization energies are defined as endothermic (energy-absorbing) steps in one direction, so this reverse reaction does not describe the second ionization energy.

Option 4: Ca2+(g) + 2e– → Ca(g). This is the full reduction of Ca2+ back to neutral calcium by two electrons, effectively the opposite of ionization processes. It does not correspond to the removal of a second electron from Ca+ to form Ca2+.

In summary, only option 1 correctly represents the second ionization step for calcium, while options 2–4 describe other processes (either multiple ionizations in one step, reverse reactions, or reduction) that do not define the second ionization energy.

Which of the following equations represents the second ionization energy of calcium? 04A单项选择题

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