Choose the process which is/are endothermic ?

Options

A. `O^(-1)+e^(-) to O^(-2)`
B. `Ar to A_(r )^(+)+e^(-)`
C. `Ar + e^(-) to Ar^(-)`
D. `H+e^(-) to H^(-)`

Answer

To determine which processes are endothermic, we need to analyze each option given in the question. An endothermic process is one that absorbs energy, resulting in a positive change in enthalpy (ΔH > 0).

### Step-by-Step Solution:

1. **Analyze the First Option: O + e⁻ → O⁻**
- This process involves the addition of an electron to an oxygen atom, forming an oxide ion (O⁻).
- The first electron gain enthalpy for oxygen is negative, indicating that this process releases energy.
- However, the second electron gain enthalpy, which is O⁻ + e⁻ → O²⁻, is positive. This means that energy is required to add a second electron to O⁻.
- **Conclusion**: The first option is endothermic.

2. **Analyze the Second Option: Ar → Ar⁺ + e⁻**
- This process involves the removal of an electron from argon, a noble gas.
- Noble gases have stable electronic configurations, and removing an electron from a stable atom requires energy.
- Therefore, this process is endothermic as it requires energy input to remove the electron.
- **Conclusion**: The second option is endothermic.

3. **Analyze the Third Option: Ar + e⁻ → Ar⁻**
- This process involves adding an electron to argon to form an argon anion (Ar⁻).
- Since argon is a noble gas with a stable electronic configuration, it does not favor gaining an electron. Energy is required to force this process to occur.
- Hence, this process is also endothermic.
- **Conclusion**: The third option is endothermic.

4. **Analyze the Fourth Option: H + e⁻ → H⁻**
- This process involves the addition of an electron to a hydrogen atom to form a hydride ion (H⁻).
- The first electron gain enthalpy for hydrogen is negative, indicating that this process releases energy.
- Therefore, this process is exothermic, not endothermic.
- **Conclusion**: The fourth option is not endothermic.

### Final Answer:
The processes that are endothermic are:
- First Option: O + e⁻ → O⁻ (endothermic)
- Second Option: Ar → Ar⁺ + e⁻ (endothermic)
- Third Option: Ar + e⁻ → Ar⁻ (endothermic)

The fourth option is exothermic.