Question

What happens to a gas when it expands, specifically how do its properties change, include at least temperature, pressure, volume, enthalpy, entropy?

Answer 1

Expansion of gases leads to in loss of internal energy, increase in volume and entropy, loss of temperature and also drop in pressure, enthalpy,

Lets have a look at some daily life example related to these:-

1. Steam coming out of pressure cooker or Kettle:- Steam inside a kettle or pressure cooker are at very high temperature and pressure but when they exits through the valve or opening provided for release of pressure you can touch the steam at some distance form valve. This is due to expansion of steam resulting in loss of Temperature and pressure. This process is similar to throttling which is also working principle of refrigerators.

From PV=Constant if P decreases V increase by same factor. as duirng expansin pressure reduces the volume increases by same factor.

Enthalpy is function of internal Energy, pressure and Volume. Due to expansion as there is loss of internal energy (function of temperature) and pressure which inturn also reduces the enthalpy of gases.

Entropy is given by dQ/T, during expansion there is loss of heat as well loss of temperature hence from the entropy relationship we can derive that there will be a increase of Entropy