Lubricant
Summary: A substance that reduces friction between moving surfaces. Tags: igcse chemistry keyword Created: 2026-08-06
A lubricant is a substance applied between two surfaces in contact to reduce friction and wear, allowing parts to slide over one another more easily. Oils are common liquid lubricants in car engines, while graphite is an important example of a solid lubricant, used in locks, bicycle chains and as a dry lubricant where liquids cannot be used.
The key IGCSE exam point explains why graphite works as a lubricant: graphite has a giant covalent layered structure in which each carbon atom is strongly bonded to three others within hexagonal layers, but the layers themselves are held together only by weak forces (London/van der Waals forces) that are large in separation. These weak forces mean the layers can slide over each other easily, reducing friction. This is the same structural feature that gives graphite its softness and flaky appearance.
Sources
- Cambridge IGCSE Chemistry 0620 Syllabus (2023-2025), Cambridge Assessment International Education
Common Misconceptions
| Misconception | Reality |
|---|---|
| All lubricants are liquids such as oil | Graphite is a solid lubricant whose layered structure allows layers to slide over each other |
| Graphite is slippery because it is soft | It is soft precisely because of its layered structure — weak forces between layers let them slide |
| Diamond and graphite would both work as solid lubricants | Only graphite works; diamond’s rigid 3D tetrahedral network is the hardest known structure and cannot slide |