
die Umsetzung
implementation
The realization or execution of a plan, idea, or project in practice.
Die Umsetzung des Bauprojekts verlief langsamer als geplant.
The implementation of the construction project went more slowly than planned.
implementation / conversion
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implementation
The realization or execution of a plan, idea, or project in practice.
Die Umsetzung des Bauprojekts verlief langsamer als geplant.
The implementation of the construction project went more slowly than planned.

conversion
In chemistry, the transformation of starting substances into new substances during a chemical reaction.
Bei der chemischen Umsetzung von Wasserstoff und Sauerstoff entsteht Energie.
Energy is produced during the chemical conversion of hydrogen and oxygen.
The noun 'die Umsetzung' (implementation/conversion) is derived directly from the verb 'umsetzen' (to implement). The verb means to put an idea or plan into action. The ending '-ung' turns the verb into a feminine noun.
Wir müssen diesen Plan so schnell wie möglich umsetzen.
We have to implement this plan as quickly as possible.
In the context of projects and plans, 'Umsetzung' (implementation) is often used with verbs such as 'gelingen' (to succeed), 'scheitern' (to fail), 'planen' (to plan), or 'vorantreiben' (to push forward). Typical adjectives are 'erfolgreich' (successful), 'schnell' (quick), or 'schrittweise' (step-by-step).
Die schrittweise Umsetzung der Reform hat begonnen.
The step-by-step implementation of the reform has begun.
To say what is being implemented, you usually use the genitive or a 'von' construction. The genitive is more common in written language.
Die Umsetzung des neuen Gesetzes erfordert Zeit.
The implementation of the new law requires time.
You can recognize the chemical meaning from signal words such as 'chemisch' (chemical), 'Stoffe' (substances), 'Reaktion' (reaction), or the names of elements. In almost all other contexts, it is about the realization of a plan.
Die vollständige Umsetzung des Zuckers in Alkohol dauert mehrere Tage.
The complete conversion of sugar into alcohol takes several days.
reaction
Both words can describe a chemical process in which substances are transformed into other substances. Reaktion refers to the process as a whole; Umsetzung is the technical term that emphasizes the transformation or consumption of the starting substances. Use Reaktion in general and Umsetzung when this change is the main focus.

Bei der Umsetzung von Wasserstoff und Sauerstoff werden die Ausgangsstoffe zu Wasser umgewandelt.
In the conversion of hydrogen and oxygen, the starting substances are transformed into water.
Bei der Reaktion von Wasserstoff und Sauerstoff entsteht Wasser.
The reaction between hydrogen and oxygen produces water.