What is the difference between entropy and enthalpy?

1 Answer
Sep 17, 2015

Example below explaining entropy and enthalpy


In a 4 stroke diesel engine, when piston takes the air into cylinder (sucks the air into cylinder) i.e. performing the first or inlet stroke while moving from top to bottom, it fully fills the cylinder with air then comes the turn of compressing this air and this compression is too much (about the ratio of 1:20) as compared with a 4 stroke petrol engine; in this process Entropy is decreased i.e. size of air is decreased without removing heat from the air (while Enthalpy remains same), this decrease in Entropy without decreasing Enthalpy i.e. without dissipating heat somewhere in the surrounding or nearby matter or environment causes a useful rise in the temperature of air about 600 degree centigrade which is more than enough to burn the diesel sprayed at that very time.