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Exergonic/Endergonic predictions via chemical equations

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In terms of entropy, if a chemical reaction is endergonic, will the reactants always have more total molecules than the products? And if exergonic, will it be the opposite, and the reactants will have more total molecules than the products?

Ex:

2C4H10 + 13O2 ---> 8CO2 + 10H2O

 

Reactants: 15 total molecules

 

Products: 18 total molecules

 

Reaction is exergonic, because the product has more total molecules than the reactants.

 

 

 

Ex 2:

CuSO4 + 2NaOH ---> Cu(OH)2 + Na2SO4

 

Reactants: 3 total molecules

 

Products: 2 total molecules

 

Reaction is endergonic, because the product has less total molecules than the reactants.


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In terms of entropy, if a chemical reaction is endergonic, will the reactants always have more total molecules than the products?

 

 

Example against your theory:

 

2H2 + O2 -> 2H2O

 

Reactants: 3 total molecules

 

Products: 2 total molecules

 

Reaction is exothermic.


Other example:

 

2 C2H2 + 5 O2 -> 4 CO2 + 2 H2O

Edited by Sensei

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Remember that the terms exothermic and endothermic refer to heat energy only, and does not include entropy effects directly.

 

There are more general energy balances, Chemists tend prefer the Gibbs Free Energy, which does include entropy in the TdS term.

Edited by studiot

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