The following processes occur in an internal combustion engine. For which one is

Question

The following processes occur in an internal combustion engine. For which one is the entropy change negative?

Compression of the gasoline/air mixture in a piston
Ignition: 2 C8H18 (octane) (g) + 25 O2 (g) --> 16 CO2 (g) + 18 H2O (g)
Expansion of hot CO2 (g) and H2O (g) in a piston
Release of CO2 (g) and H2O (g) into the air
All of these have a positive entropy change.

Explanation / Answer

5) All of these have a positive entropy change. Reversible process of expansion and compression have zero entropy, ?S = 0, so it impossible for 0 > ?S --> 1) and 3) are false Chemical reaction will also has positive change of entropy --> 2) false CO2 and H20 gasses have pressure higher than atmospheric, so it has certain availability to perform work. If they release to the air, then their availability decrease, it means increase of entropy. 4) false

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