# Dew point and absolute humidity

• Karol
In summary, the absolute moisture at a room temperature of 200C and relative humidity of 60% can be calculated by first finding the vapor pressure, given by 10.5 mm Hg, and then using the ideal gas law with a pressure of 10.5/760 atm and a volume of 1 liter. This results in an absolute moisture of 10.3 gr/m3.
Karol

## Homework Statement

Room temperature is 200C and relative humidity is 60%. what is the absolute moisture

## Homework Equations

Vapor pressure at 200C=17.5[atm]
PV=nRT
Molecular weight of water=18[gr/mol]

## The Attempt at a Solution

The vapor pressure at 200C:
$$\frac{x}{17.5}=0.6\rightarrow x=10.5[atm]$$
$$PV=nRT\rightarrow 10.5\cdot 1=n\cdot 0.08208\cdot 293\rightarrow n=0.437[mol]$$
$$0.437\cdot 18=7.86[\frac{gr}{m^3}]$$
It should be 10[gr/m3]

Karol said:

## Homework Statement

Room temperature is 200C and relative humidity is 60%. what is the absolute moisture

## Homework Equations

Vapor pressure at 200C=17.5[atm]
That should be mm Hg.
PV=nRT
Molecular weight of water=18[gr/mol]

## The Attempt at a Solution

The vapor pressure at 200C:
$$\frac{x}{17.5}=0.6\rightarrow x=10.5[atm]$$
Again, that should be mm Hg
$$PV=nRT\rightarrow 10.5\cdot 1=n\cdot 0.08208\cdot 293\rightarrow n=0.437[mol]$$
$$0.437\cdot 18=7.86[\frac{gr}{m^3}]$$

The gas constant value you used here for liters. You also need to use a pressure of 10.5/760 atm.

Chet

$$\frac{x}{0.023}=0.6\rightarrow x=0.0138[atm]$$
$$PV=nRT\rightarrow 0.0138\cdot 1[liter]=n\cdot 0.08208\cdot 293\rightarrow n=0.000574[\frac{mol}{liter}]=0.574[\frac{mol}{m^3}]$$
$$0.574\cdot 18=10.3[\frac{gr}{m^3}]$$

Karol said:
$$\frac{x}{0.023}=0.6\rightarrow x=0.0138[atm]$$
$$PV=nRT\rightarrow 0.0138\cdot 1[liter]=n\cdot 0.08208\cdot 293\rightarrow n=0.000574[\frac{mol}{liter}]=0.574[\frac{mol}{m^3}]$$
$$0.574\cdot 18=10.3[\frac{gr}{m^3}]$$
Excellent!

Chet

I would like to clarify that the calculation provided is correct, but it is not the absolute moisture. The term "absolute moisture" is not commonly used in scientific literature. The correct term for the amount of water vapor in a given volume of air is "absolute humidity." The calculation provided gives the absolute humidity in units of grams per cubic meter (g/m3). Therefore, the absolute humidity at 20°C and 60% relative humidity is approximately 7.86 g/m3.

## 1. What is the difference between dew point and absolute humidity?

Dew point is the temperature at which water vapor in the air will condense into liquid water. Absolute humidity, on the other hand, is a measure of the total amount of water vapor present in the air.

## 2. How are dew point and absolute humidity related?

Dew point and absolute humidity are related because as the temperature increases, the air can hold more water vapor. This means that as absolute humidity increases, so does the dew point.

## 3. Why is dew point important?

Dew point is important because it is a key indicator of the amount of moisture in the air. It can help predict the formation of fog, dew, and precipitation, and can also affect human comfort and the growth of plants and crops.

## 4. How is dew point measured?

Dew point is typically measured using a hygrometer, which measures the amount of water vapor in the air. This information is then used to calculate the dew point temperature.

## 5. What is a comfortable dew point for humans?

The ideal dew point for human comfort is between 50 and 60 degrees Fahrenheit. Higher dew points can make the air feel more humid and uncomfortable, while lower dew points can make the air feel dry and uncomfortable.

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