At a weather recording station, the air temperature is 25^\circ\text{C} and the relative h… — JAMB UTME

At a weather recording station, the air temperature is $25^\circ\text{C}$ and the relative humidity is recorded as $60\%$ . If the saturated vapour pressure of water at $25^\circ\text{C}$ is $24.0\text{ mmHg}$ , what is the actual partial vapour pressure of water present in the atmosphere?

$14.4\text{ mmHg}$ Answer
B
$40.0\text{ mmHg}$
C
$9.6\text{ mmHg}$
D
$24.0\text{ mmHg}$

Answer

The actual partial vapour pressure of water present in the atmosphere is

14.4\text{ mmHg}

Relative humidity is defined as the ratio of actual partial vapour pressure to saturated vapour pressure at the same temperature, expressed as a percentage. Therefore, the actual partial vapour pressure is

60\%

24.0\text{ mmHg}

, which equals

14.4\text{ mmHg}

Step-by-Step Solution

State the standard relationship defining relative humidity in terms of vapour pressures.

\text{Relative Humidity (R.H.)} = \frac{\text{Partial Vapour Pressure}}{\text{Saturated Vapour Pressure at Air Temp}} \times 100\%

Relative humidity quantifies how close the air is to maximum moisture saturation at a given temperature.

Substitute the given numerical values into the relative humidity formula.

60\% = \frac{P}{24.0\text{ mmHg}} \times 100\%

Here

P

represents the unknown actual partial vapour pressure of water in the atmosphere.

Rearrange the equation to isolate and solve for

P

P = 0.60 \times 24.0\text{ mmHg} = 14.4\text{ mmHg}

Multiplying the saturated vapour pressure by

0.60

yields the actual partial vapour pressure.

Key Concept

Relative Humidity and Vapour Pressure Calculation

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