Cfrgtkky

Because my setting is incredibly varied, I've been advised against attempting to ask this in a single question, and have broken this up into a series. Each context will be roughly analogous to a setting in my world(s).

Imagine that you live in France during the stone age. One day, you and five friends have the ability to magically induce redox reactions at-will.

Each person can use this ability to effect a total mass of 3 tons, per day. They can control the speed of the reaction, the scale of the reaction and remove the need for any activation energy.

The goal of you and your friends is to exert economic dominance over neighboring tribes using the least amount of this power.

You and your friends are in complete agreement about this goal and the means of achieving it. Nobody will be founding new religions around you or your powers. You have no foreknowledge of history. There are no particularly important figures for you to assassinate. Your environment and tools are otherwise typical of the time and place. The power can be used on yourselves, inanimate objects, and non-human animals.

How would you do this?

Stone age means all the tribes around you still use stone tools.

With your redox ability you can reduce metal oxides to native metals. One among the others: take those yellow looking stones which your descendant will call limonite and turn them to iron.

Now you can produce and sell metallic objects: swords, axes, arrows, knives, spades... just be sure to sell to every tribe, so that they maintain a sort of balance of power (you don't want a single strong side to emerge and see you as a threat to their ruling and therefore attempt to get rid of your power).

Whenever someone tries to trick you or to overthrow the balance you created, you can "magically" oxidize their metal back, just to make clear who is in charge.

Photosynthesis counts as a redox reaction. Since you have said that all activation energy is negated, sunlight's natural limit on the growth rate of plants can be removed, meaning that your characters can speed up the growth rate of crops and keep them growing in all seasons of the year. However, gas and liquid transfer rates (through the stomata and the roots, respectively) do impose a natural limit on how quickly the plants can undergo their redox reactions, so they can't instantly grow to maturity, but they will most definitely form a faster and more stable source of food, which would allow your characters to form a powerful agricultural economy for the times.