Is Cl2 + 2e- -> 2Cl- an oxidation half-reaction?

Oxidation is the loss of electrons. Did it lose electrons? Looks like it gained electrons to me.

Almost. It will be written as 2Cl- -> Cl2 + 2e-

I think it is an oxidation reaction because it gained electrons (the ones on the product side). It went from -1 to 0 (which is an increase in nox).

To determine if a half-reaction is an oxidation half-reaction, you need to assess whether the element in the reactant is losing electrons (being oxidized) or gaining electrons (being reduced). Here's how you can analyze the given half-reaction, Cl2 + 2e- -> 2Cl-:

1. Identify the element undergoing oxidation and reduction. In this case, the element is chlorine (Cl).

2. Compare the oxidation states of chlorine in the reactant and product. In Cl2, the oxidation state of chlorine is 0 because elemental chlorine has no charge. In Cl-, the oxidation state of chlorine is -1 because chloride ions have a charge of -1.

3. Determine the change in oxidation state. The oxidation state of chlorine changes from 0 to -1, indicating that it gains electrons. When an element gains electrons, it undergoes reduction.

Therefore, the given half-reaction, Cl2 + 2e- -> 2Cl-, shows reduction, not oxidation.