entropy q (from destroyer)

[Tina324]

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Which has greater entropy..C4H10 or C3H8?
why?

thanks!!!

 

[Tina324]

Another one:

#30 from a true/false gchem destroyer question
"All spontaneous rxns result in an increase in entropy of the universe" =True

How the heck is this true? If we look at the deltaG=deltaH-TdeltaS equation, a rxn can be spontaneous if entropy is negative (as long as enthalpy is negative).

Am I right??

 

[Contach]

I would say that you would have to break this down into 2 questions depending on the question:

Intermolecular -
C3H8 has more entropy if you are talking about a solution of this. We know that as the Alkanes go lower, they are more likely to be in their gas state. Therefore there is more disorder in gas, and thus higher entropy than C4H10, which would be closer towards the solid spectrum of alkanes.

Intramolecular -
C4H10 has more intramolecular entropy. Becuase 1 C4H10 molecule has more bonds and rotations than a C3H8 does. Therefore there is more disorder in C4H10 than C3H8. Thus C4H10 has a higher intramolecular enropy.

 

[Xtian]

C4, the more atoms, the greater the entropy

Remember, the entropy of the universe is increasing.

 

[wifi08]

C4H10 has more entropy
also why do you question that rule,. its one of the three laws of thermodynamics; know it

 

[Tina324]

thanks for the help guys.

in regards to the 2nd question, of course the entropy of the universe is always increasing, but using the gibbs free energy equation, a rxn CAN be spontaneous if the entropy is negative, as long as the enthalpy is negative as well (and temp is low)....so how do we explain this?

 

[chessxwizard]

You're thinking about the entropy of isolated systems. While reactions can occur spontaneously even with a decrease in entropy, the entropy of the universe is constantly increasing.