Question

The vapor pressure of water at 10 °C is 1300 Pa. (a) What percentage of atmospheric pressure is this? Take atmospheric pressure to be 1.013 × 105 Pa. (b) What percentage of the total air pressure at 10 °C is due to water vapor when the relative humidity is 100%? (c) The vapor pressure of water at 20 °C is 2500 Pa. What is the relative humidity at this temperature if the partial pressure of water in the air has not changed from what it was at 10 °C when the relative humidity was 100%?

Answer 1

The vapor pressure of water at 20.0°C is 2.33 x 10³ Pa, which corresponds to 2.31% of atmospheric pressure. At 100% relative humidity, the percentage of water vapor in the air at 20.0°C is 17.2%.

Step-by-step explanation:

(a) The vapor pressure of water at 20.0°C is 2.33 x 10³ Pa.

(b) To find the percentage of atmospheric pressure, we divide the vapor pressure by the atmospheric pressure and multiply by 100:

(2.33 x 10³ Pa / 1.01 × 10⁵ Pa) x 100 = 2.31%

So, the vapor pressure of water at 20.0°C corresponds to 2.31% of atmospheric pressure.

(c) If the relative humidity is 100%, the percentage of water vapor in the air at 20.0°C is equal to the vapor density of water at that temperature.

So, according to Table 13.5, the saturation vapor density is 17.2 g/m³.

Therefore, the percentage of water vapor in the air is 17.2% at 100% relative humidity.