Dew point and absolute humidity

[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]

 

[Chestermiller]

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

 

[Karol]

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

 

[Chestermiller]

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

Excellent!

Chet