# Basement humidor

BuffaloTraceBuckeye
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im running a cigar oasis in a 300 ct humidor I have about 250 sticks in there . My basement stays cooler 63-64 degrees . I have been keeping my sticks at 69 percent. They seem a little dry and minor draw issues can I bump up the cigar oasis to about 72 percent ??

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## Comments

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vaporization curves of most liquids have similar shapes. The vapor pressure steadily increase as the temperature increases. A good approach is to find a mathematical model for the pressure increase as a function of temperature. Experiments showed that the vapor pressure PP and temperature TT are related,where

If P1P1 and P2P2 are the vapor pressures at two temperatures T1T1 and T2T2, then a simple relationship can be found:

This is known as the Clausius-Clapeyron Equation and allows us to estimate the vapor pressure at another temperature, if the vapor pressure is known at some temperature, and if the enthalpy of vaporization is known.

ALTERNATIVE FORMULATION

Note the order of the temperatures in Equation 1.21.2 matters as the Clausius-Clapeyron Equation is often written with a negative sign (and switched order of temperatures):

EXAMPLE 1.11.1: VAPOR PRESSURE OF WATER

The vapor pressure of water is 1.0 atm at 373 K, and the enthalpy of vaporization is 40.7 kJ mol-1. Estimate the vapor pressure at temperature 363 and 383 K respectively.

SOLUTION

Using the Clausius-Clapeyron equation (Equation 1.21.2), we have:

Note that the increase in vapor pressure from 363 K to 373 K is 0.303 atm, but the increase from 373 to 383 K is 0.409 atm. The increase in vapor pressure is not a linear process.

DiscussionWe can use the Clausius-Clapeyron equation to construct the entire vaporization curve. There is a deviation from experimental value, that is because the enthalpy of vaporization various slightly with temperature.

The Clausius-Clapeyron equation can be also applied to sublimation; the following example shows its application in estimating the heat of sublimation.

EXAMPLE 1.21.2: HEAT OF SUBLIMATION OF ICE

The vapor pressures of ice at 268 K and 273 K are 2.965 and 4.560 torr respectively. Estimate the heat of sublimation of ice.

SOLUTION

The enthalpy of sublimation is ΔHsubΔHsub. Use a piece of paper and derive the Clausius-Clapeyron equation so that you can get the form:

Note that the heat of sublimation is the sum of heat of melting and the heat of vaporization.

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1,676✭✭✭✭✭EXERCISE 1.21.2

Show that the vapor pressure of ice at 274 K is higher than that of water at the same temperature. Note the curve of vaporization is also called the curve of evaporization.

EXAMPLE 1.31.3: HEAT OF VAPORIZATION OF ETHANOL

Calculate ΔHvapΔHvap for ethanol, given vapor pressure at 40 oC = 150 torr. The normal boiling point for ethanol is 78 oC.

SOLUTION

Recognize that we have TWO sets of (P,T)(P,T) data:

Substituting into the above equation twice produces:

and

Subtract these two equations, to produce:

Solving for ΔHvapΔHvap :

ADVANCED NOTE:

It is important to not use the Clausius-Clapeyron equation for the solid to liquid transition. That requires the use of the more general Clapeyron equation

where ΔH¯ΔH¯ and ΔV¯ΔV¯ is the molar change in enthalpy (the enthalpy of fusion in this case) and volume respectively between the two phases in the transition.

## Contributors

Chung (Peter) Chieh (Chemistry, University of Waterloo)

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