Water Damage Restoration Technician (WRT) Certification Practice Test

What has the lowest vapor pressure in the following conditions: 80°F at 60% RH or 53°F at 80% RH?

1. 80°F at 60% RH

2. 53°F at 80% RH

3. Both have the same vapor pressure

4. Cannot be determined

The correct answer is: 53°F at 80% RH

To understand why the condition of 53°F at 80% relative humidity has the lowest vapor pressure, we need to consider the definitions of vapor pressure, temperature, and relative humidity. Vapor pressure refers to the pressure exerted by a vapor in equilibrium with its liquid or solid form. As temperature increases, the ability of water molecules to escape into the vapor phase also increases, resulting in higher vapor pressure. Conversely, lower temperatures typically correspond to lower vapor pressures. In the given scenarios, at 80°F with 60% relative humidity, the air holds a significant amount of moisture but is also at a higher temperature, which facilitates higher vapor pressure compared to cooler conditions. At 53°F with 80% relative humidity, even though the relative humidity is higher, the temperature is significantly lower. In lower temperature conditions, the capacity of the air to hold water vapor is reduced, leading to a lower actual vapor pressure despite the higher relative humidity percentage. This relationship indicates that while relative humidity gives an idea of how saturated the air is at a certain temperature, it doesn’t directly represent the actual amount of moisture present in absolute terms, especially when paired with temperature differentials. Therefore, the condition at 53°F under 80% relative humidity results