A Level Chemistry OCR Practice Exam

Which of the following best defines an addition reaction?

1. A reaction where an unsaturated molecule is converted to a saturated molecule

2. A reaction where a gas or liquid binds to a solid surface

3. A process involving hydrocarbons in a straight chain

4. A reaction that forms a hydrocarbon ring structure

The correct answer is: A reaction where an unsaturated molecule is converted to a saturated molecule

An addition reaction is characterized as a reaction where an unsaturated molecule, which contains double or triple bonds, is converted into a saturated molecule, typically by adding atoms or groups of atoms across the multiple bonds. This process leads to the saturation of the molecule, effectively removing the unsaturation by breaking these multiple bonds and adding new atoms, often resulting in the formation of alkanes from alkenes or alkynes. The other options don't accurately define addition reactions. The binding of a gas or liquid to a solid surface refers to adsorption, which is not related to the chemical transformation of molecules. The description involving hydrocarbons in a straight chain does not specify the characteristics of addition reactions, as they can occur in various molecular structures. Lastly, forming a hydrocarbon ring structure pertains to cyclization or polymerization processes rather than the addition of atoms across unsaturated bonds.