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When electrons are being added/removed from atoms or ions how can I tell if the process is exothermic or endothermic? For example in the question below, how could I tell for sure which of the processes are exothermic and which are endothermic?

$\ce{Ca -> Ca+ + e–}$

$\ce{I + e– -> I–}$

$\ce{O– + e– -> O^{2–}}$

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  • $\begingroup$ How much you already know about this topic? $\endgroup$ – Mithoron Aug 7 '20 at 21:21
  • $\begingroup$ Your title needs work! $\endgroup$ – user55119 Aug 7 '20 at 22:23
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You need to know that thermodynamics are greatly affected by state. Hence you need to give precise states of all the reactants and compounds. Ca(g)⟶Ca+(g)+e− and Ca(s)⟶Ca+(s)+e− has quite a difference.

Secondly for any element, ionization energy is always endothermic. Let me define ionization energy.

Ionization Energy is the energy required to remove one mole of electrons from one mole of gaseous atoms or ions. X⟶X+(g)+e− Enthalpy Change = positive Hence process is endothermic

Electron affinity is the enthalpy change which occurs when a mole of electrons combine with a mole of gaseous ions or atoms. X(g)+e−⟶X-(g) Now, electron affinity depends on the element under study. This webpage mentioned below will give detailed insight about electron affinity and its trends.

https://byjus.com/chemistry/electron-affinity/

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