International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What explains the time delay in gas particles diffusing across a room?

1. Gas particles collide with air particles and move randomly

2. Gas particles adhere to surfaces

3. Gas particles travel in a straight line without collisions

4. Gas particles are too large to move quickly

The correct answer is: Gas particles collide with air particles and move randomly

The time delay in gas particles diffusing across a room can be attributed to the nature of their movement, which is random and involves collisions. Gas particles are in constant motion and travel in straight lines until they collide with other particles, such as air molecules. These collisions cause the gas particles to change direction, leading to a zigzag path rather than a direct route from one side of the room to the other. The random nature of these movements and frequent collisions create delays in how quickly a gas can spread out across a given space. In contrast, the other factors listed do not adequately account for the delay. Gas particles do not have significant adhesion to surfaces that would influence their diffusion in the same way as a solid or liquid might; thus, the second option does not apply. The notion that gas particles travel exclusively in straight lines without collisions is incorrect, as collisions are a fundamental characteristic of gas behavior. Finally, gas particles are typically not too large to move quickly; on the contrary, they are quite small and move rapidly, so size is not the reason for any delays in diffusion.