Final answer:
In physics, at 20.0°C, the vapor pressure of water is typically around 2.33 kPa, which is approximately 2.3% of the standard atmospheric pressure. The concept of relative humidity indicates the amount of water vapor present in the air compared to the maximum amount the air can hold at that temperature, and 100% relative humidity means air at a given temperature contains the maximum amount of water vapor it can hold.
Step-by-step explanation:
The student's multi-part question pertains to atmospheric conditions such as room temperature, atmospheric pressure, and relative humidity, which are all fundamental topics in the field of physics, specifically in the area of thermodynamics. The questions require knowledge of how to calculate vapor pressure, understanding the proportion of vapor pressure in relation to atmospheric pressure, and comprehending the concept of relative humidity and how it changes with temperature.
(a) The vapor pressure of water at 20.0°C can be found in steam tables or calculated using the Clausius-Clapeyron relation, but typically, it's approximately 2.33 kPa. (b) To find what percentage of atmospheric pressure this corresponds to, we compare the vapor pressure to the standard atmospheric pressure, which is about 101.3 kPa, resulting in approximately 2.3%. (c) The percent of 20.0°C air that is water vapor if it has 100% relative humidity can be determined considering the mass of the water vapor and the density of dry air, which leads us to calculate that the air contains a certain mass percentage of water vapor.
When analyzing relative humidity changes with temperature, we must understand that as temperature increases, the air can hold more water vapor, and thus the relative humidity decreases if the actual vapor density remains constant. Conversely, if the temperature decreases and the vapor density remains unchanged, the relative humidity increases, as the saturation vapor pressure decreases with temperature.