The molar enthalpy change accompanying the removal of an electron from a gas phase atom or ion in its ground state is called?

Analyze the question

The question asks for the name of the energy change when an electron is removed from a gaseous atom or ion in its ground state.

Explain the concept

• Ionization enthalpy (ionization energy) is the energy required to remove an electron from a gaseous atom or ion in its ground state. • First ionization enthalpy: X(g) → X⁺(g) + e⁻ • Second ionization enthalpy: X⁺(g) → X²⁺(g) + e⁻
• It is always endothermic (ΔH is positive), because energy must be supplied to overcome the nucleus's attraction for the electron.
• Electron gain enthalpy (electron affinity) is the opposite process. It is the enthalpy change when an electron is added to a gaseous atom.

Go through the options

• A. Electron gain enthalpy: This is about adding an electron, so it is wrong.
• B. Ionization enthalpy: This is about removing an electron from a gaseous atom or ion, so it matches the definition.
• C. Enthalpy change: This is too general. It refers to any heat change at constant pressure, so it is wrong.
• D. Enthalpic gas removal: This is not a real chemistry term, so it is wrong.

Answer: The correct option is B. Ionization enthalpy.

Exam tip: Look at the key words in the definition. "Removal of an electron" together with "gaseous" always points to ionization energy. "Gain" or "addition" of an electron points to electron affinity. Also remember that the state symbol (g) matters in these definitions.