Q. What is Entropy?

Ans.

The strangest thing about entropy is that it is denoted by the letter S.

Entropy is the measure of the disorder in a system. A system with low entropy is very orderly. A system with high entropy is extremely messy and chaotic.

 The picture on the left has low entropy while the system on the right has higher entropy.

When you clean up the house it has less entropy, but, as you know, it tends to get messy rather quickly.  It may be comforting to know that this is the natural path for most spontaneous reactions.  Moving from order to disorder, low entropy to high entropy, is generally a spontaneous process, So take comfort, the messiness of your house is almost inevitable.

Change in entropy is calculated in the same way that change in temperature is calculated.

ΔS = S_products - S_reactans

A spontaneous process will tend to have a positive ΔS , representing an increase in disorder. The following are spontaneous processes with a positive value of ΔS.