What is the term for heat transfer that occurs between closely packed molecules?

The term for heat transfer that occurs between closely packed molecules is conduction. This process involves the transfer of thermal energy through direct contact between neighboring molecules or atoms. Essentially, in conduction, when one part of a substance is heated, the molecules in that region gain energy and vibrate more vigorously. These energized molecules collide with adjacent, less energetic molecules, transferring some of their energy to them. This mechanism is effective in solids, where molecules are closely packed together, allowing for efficient energy transfer.

In contrast, convection refers to heat transfer through fluid movement, where warmer regions of a fluid rise and cooler areas sink, creating a current. Radiation involves the transfer of heat through electromagnetic waves, which does not require a medium to propagate, such as the heat from the sun reaching the Earth. Diffusion relates to the movement of particles from an area of high concentration to an area of low concentration and does not specifically pertain to heat transfer. Thus, conduction is correctly identified as the appropriate term for heat transfer between closely packed molecules.