Humber Admissions Practice Test

What is a combination reaction?

1. A reaction producing two new substances

2. A reaction that forms a single new substance from multiple reactants

3. A reaction where a compound breaks down into simpler substances

4. A reaction where one element displaces another

The correct answer is: A reaction that forms a single new substance from multiple reactants

A combination reaction is characterized by the formation of a single new substance from two or more reactants. In this type of reaction, the reactants, which can be elements or compounds, combine together to create one distinct product. This is often represented by a balanced chemical equation where the total number of atoms of each element is conserved, ensuring that the mass is balanced on both sides of the equation. For instance, when hydrogen gas combines with oxygen gas, they form water, which is a single new substance. This clear transformation from multiple reactants into one product is the hallmark of combination reactions, distinguishing them from other types of chemical reactions such as decomposition, where a single compound breaks down into simpler substances, or displacement reactions, where one element replaces another in a compound.