To answer this question, let's dive into a brief explanation of what humidity is and how it affects the density of air.
Humidity refers to the amount of water vapor present in the air. Relative humidity is the ratio of the current absolute humidity to the highest possible absolute humidity at that temperature, expressed as a percentage. Higher relative humidity means that the air holds more water vapor.
Now, dry air is primarily composed of nitrogen and oxygen, which have molecular masses of about 28 and 32 atomic mass units respectively. Meanwhile, water vapor (H2O), with a molecular mass of about 18 atomic mass units, is much lighter than nitrogen and oxygen. This means that when you introduce water vapor into dry air, you are effectively replacing some heavier molecules with lighter ones. Consequently, the mixture of air and water vapor will be less dense than dry air at the same temperature and pressure.
So, given the same temperature of 80° C, let's consider the two scenarios presented:
- 80% relative humidity air: This air has a higher proportion of water vapor mixed with the dry air, meaning a greater fraction of lighter molecules (H2O).
- 20% relative humidity air: This air has a lower proportion of water vapor, meaning that the air mostly consists of heavier molecules (nitrogen and oxygen).
Based on this understanding:
- The air at 80% relative humidity will have a higher proportion of water vapor (lighter molecules), making it less dense compared to drier air at 20% relative humidity.
- The air at 20% relative humidity will mostly contain the heavier nitrogen and oxygen molecules, making it denser compared to the more humid air at 80% relative humidity.
Therefore, the correct statement regarding the density of air with different relative humidity levels at the same temperature is:
C) The 80% relative humidity air will be less dense.
