Concept: The spread of smell from one place to another involves the movement of particles. Several physical processes can contribute to this. Step 1: Understanding the nature of smell and hot food
The smell of food comes from volatile (easily vaporized) aromatic compounds present in the food. When food is hot, these compounds vaporize more readily and mix with the air. Step 2: Analyzing the given processes
(1) Boiling: Boiling is the process where a liquid turns into vapor rapidly throughout the bulk of the liquid when it reaches its boiling point. While cooking might involve boiling water, the spread of smell itself is not boiling.
(2) Evaporation: Evaporation is a surface phenomenon where a liquid changes into vapor at a temperature below its boiling point. Hot food will have its volatile components evaporating into the air. This is a crucial first step for the smell to become airborne.
(3) Sublimation: Sublimation is the direct transition of a substance from solid to gas without passing through the liquid phase. This is not the primary process for the smell of most cooked food.
(4) Diffusion: Diffusion is the process of spontaneous intermixing of particles of different substances due to their random motion. Once the aromatic particles from the hot food evaporate and mix with the air in the kitchen, these gaseous particles (air mixed with aroma molecules) move from an area of higher concentration (the kitchen) to areas of lower concentration (outside the house). This movement and spreading out of the aroma particles through the air is diffusion. Step 3: Identifying the primary reason for the smell spreading
While evaporation allows the aromatic compounds to become airborne, the process by which these airborne particles spread out over a distance to be smelt outside the house is diffusion. The kinetic energy of the gas molecules (both air and the aroma molecules) causes them to move randomly and spread out, eventually reaching an observer outside. Hot food particles have higher kinetic energy, which speeds up both evaporation and diffusion. Therefore, diffusion is the primary reason the smell of hot food can be detected far from its source.