O_(g) +e = O^- EA1= negative

O_(g) + e =O2^- EA2= positive

write the equation for the overall electron affinity , is the overall electron affinity positive or negative? Give reasons.

To tackle the question of overall electron affinity based on the provided equations, let's break down the concepts involved and derive the overall equation step by step.

Understanding Electron Affinity

Electron affinity refers to the energy change that occurs when an electron is added to a neutral atom in the gas phase. This process can either release energy (negative electron affinity) or require energy (positive electron affinity). The equations you've provided illustrate two different scenarios for the addition of electrons to oxygen (O).

Analyzing the Given Equations

Let's look closely at the equations:

• O (g) + e = O^- (g) - EA1 = negative
• O^- (g) + e = O₂ (g) - EA2 = positive

In the first equation, the addition of an electron to a neutral oxygen atom results in the formation of an oxide ion (O^-). This process has a negative electron affinity (EA1), indicating that energy is released when the electron is added. This is typical for nonmetals like oxygen, which readily accept electrons.

In the second equation, the negatively charged oxide ion (O^-) gains another electron to form a neutral O₂ molecule. This process has a positive electron affinity (EA2), meaning energy must be supplied to add the electron to the already negatively charged ion.

Combining the Reactions

To find the overall electron affinity, we can combine these two reactions. The overall reaction can be represented as:

O (g) + 2e = O₂ (g)

Now, let's express the overall electron affinity (EA_overall):

EA_overall = EA1 + EA2

Determining the Sign of Overall Electron Affinity

Now, we need to analyze the signs of EA1 and EA2:

• EA1 is negative (exothermic process).
• EA2 is positive (endothermic process).

Since EA1 is negative, it contributes a negative value to the overall electron affinity. EA2, being positive, adds a positive value. The overall sign of EA_overall will depend on the magnitudes of EA1 and EA2.

Conclusion on Overall Electron Affinity

If the magnitude of EA1 (the energy released when the first electron is added) is greater than the magnitude of EA2 (the energy required to add the second electron), then the overall electron affinity will be negative. Conversely, if EA2 is greater, the overall electron affinity will be positive. In most cases for oxygen, the first electron addition is significantly more favorable than the second, suggesting that the overall electron affinity is likely to be negative.

In summary, the overall electron affinity for the process of adding two electrons to oxygen is generally negative, indicating that the formation of O₂ from O (g) and two electrons is energetically favorable, primarily due to the strong attraction of the first electron to the oxygen atom.