Final answer:
The chemical union of water with another substance is called hydrolysis, which breaks down complex molecules into simpler ones and is fundamental in biological and chemical processes.
Step-by-step explanation:
The chemical union of water with another substance is called hydrolysis. In this process, a water molecule is split into a hydrogen ion (H+) and a hydroxyl ion (OH-) which then interact with the other substance. This type of reaction is crucial in biology and chemistry as it aids in breaking down complex molecules into simpler ones. An example of hydrolysis in action is the digestion of food, where large nutrient molecules are broken down into smaller components that can be absorbed by the body.
By contrast, in a dehydration synthesis (also known as a condensation reaction), the combination of two molecules results in the formation of a new molecule and the release of a molecule of water. This is the opposite process of hydrolysis and is equally important for the formation of large macromolecules such as proteins and carbohydrates from their smaller building blocks.