Humber Admissions Practice Test

Which of the following reactions is not considered a double-displacement reaction?

1. AgNO3 + NaCl → AgCl + NaNO3

2. H2 + O2 → H2O

3. BaCl2 + Na2SO4 → BaSO4 + 2NaCl

4. NaOH + HCl → NaCl + H2O

The correct answer is: H2 + O2 → H2O

A double-displacement reaction, also known as a metathesis reaction, involves the exchange of ions between two compounds, typically resulting in the formation of a new compound and the exchange partners. In the correct example, the reaction H2 + O2 → H2O does not fit this definition, as it is a combination reaction where two elements combine to form a single product (water). This type of reaction showcases elements coming together, rather than trading components between two separate compounds. In contrast, the other reactions listed involve the exchange of ions or components. For instance, in the first reaction involving silver nitrate and sodium chloride, silver ions and chloride ions exchange partners to form silver chloride and sodium nitrate. Similarly, the reaction with barium chloride and sodium sulfate, and the reaction between sodium hydroxide and hydrochloric acid, each involve the exchange of ions leading to the formation of new products. Hence, only the reaction between hydrogen and oxygen stands out as one that does not involve this exchange of ions, confirming it as the one not classified as a double-displacement reaction.