Chemistry: why clotheslines can still work in winter, part1
Tutoring chemistry, interesting applications can come up. The tutor mentions one connected with Gibbs free energy.
In my previous post I mention Gibbs free energy and how it can be used to predict spontaneity. Specifically, if Gibbs free energy decreases from a process, said process is predicted to be spontaneous.
Clothes drying on a clothesline in winter can serve as as interesting illustration of Gibbs free energy. Although drying clothes is a physical change, not chemical, it can still serve as a case for the Gibbs free energy model.
The theory is that, even when the outdoor temp remains below zero Celsius, negative 5°C, for instance, laundered clothes hung outdoors to dry will eventually do so. They will even freeze first, perhaps, but then be dry at some point afterwards.
Gibbs free energy can predict that said drying process can work, as follows:
G=H-TS, for a change, becomes ΔG=ΔH-TΔS
(See my previous post for the definitions of parameters.)
Intuitively, people realize that, for said process to work, the enthalpy (H) actually has to increase. Since enthalpy is related to heat, it seems hard to imagine, at -5°C, how it can.
Yet, even under such conditions, there is enough environmental energy (from sunlight, for instance) to raise the enthalpy of a water molecule here and there. Importantly, the increase of entropy (disorder) from being frozen in ice to a free-moving vapour molecule is significant.
In ΔG=ΔH-TΔS, T is absolute temperature. Therefore, at -5°C, T is 268K.
Note that in a closed system, where heat cannot enter, such process likely wouldn’t work. Yet, with an open system, such as outdoors in winter, heat energy is always capable of arriving or leaving.
Source:
White, J.E. (1987). Physical Chemistry. Books for Professionals, Inc.
Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.