Is there any significance of entropy and enthalpy in IC Engines?

Answer 1

Yes, knowing these values for the combusion of the fuel used on the internal combustion engine (ICE) will help you determine the maximum amount of energy which may be extracted from the engine and then from that, the engine's efficiency.

The maximum amount of energy which may be extracted out of a chemical reaction (the max work the reaction can do) can be calculated by finding the reactions change in the Gibbs free energy under the conditions which the reaction is under.

The Change in the Gibbs Free Energy (delta G) can be calculated as,
(delta G) = (delta H) - T*(delta S)
Where (delta H) is the change in the enthalpy of the reaction, T is the temperature of the reaction in Kelvin, and (delta S) is the change in entropy of the reaction.

If the value of (delta G) comes out to be <0 (i.e negative), then the reaction is spontaneous under those conditions and work can be extracted up to the magnitude of the change in Gibbs free enery.
If the value of (delta G) is greater than zero (positive) then the reaction is not spontaneous and requires that much energy to be put INTO the system in order for the reaction to proceed under those conditions. In this case, no work can be extracted, work actually needs to be spent in order to get the reaction to occur.