A substance that slows, or even stops a chemical reaction is called a ____________________.

A substance that slows down or stops a chemical reaction is called a inhibitor. Inhibitors can work through various mechanisms, including the bonding to enzymes or catalysts, thereby reducing their activity. This is particularly critical in biochemical processes, where the regulation of enzymatic activity is necessary for maintaining homeostasis within living organisms. Inhibitors are not limited to biological reactions but are also an integral part of industrial processes where they can prevent unwanted side reactions, thus increasing product yield and safety. For example, in the context of pharmaceuticals, inhibitors can be designed to target specific enzymes in pathogens, effectively stopping the progression of disease.