Chemistry – States of matter - Diffusion | e-Consult
States of matter - Diffusion (1 questions)
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The student would observe the following diffusion rates: carbon dioxide (Mr = 44)
Explanation using Kinetic Molecular Theory:
- Average Speed: The kinetic molecular theory states that the average kinetic energy of gas molecules is directly proportional to the absolute temperature and inversely proportional to the molar mass. Therefore, lighter molecules (lower Mr) have higher average speeds than heavier molecules (higher Mr) at the same temperature.
- Diffusion Rate and Speed: The rate of diffusion is directly proportional to the average speed of the gas molecules. Faster-moving molecules diffuse more quickly.
- Relationship between Mr and Speed: Since lighter molecules have higher average speeds, they diffuse faster. Conversely, heavier molecules diffuse slower. The relationship is not linear; the effect of molar mass on diffusion rate is proportional to the square root of the molar mass. This is because the speed of the molecules is proportional to the square root of the molar mass.
Therefore, carbon dioxide, with the highest molar mass, has the lowest average speed and thus the slowest diffusion rate. Nitrogen, with the lowest molar mass, has the highest average speed and the fastest diffusion rate. Oxygen falls in between, exhibiting an intermediate diffusion rate.