## entropy sign

$\Delta S = \frac{q_{rev}}{T}$

Posts: 52
Joined: Fri Sep 29, 2017 7:03 am

### entropy sign

How can we tell the sign of entropy based off a chemical equation?

Julianna Thrasher 1B
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Joined: Thu Jul 27, 2017 3:00 am

### Re: entropy sign

You can look at the phases of all substances in the chemical reaction. Entropy increases from solid --> liquid --> gas since entropy is a measure of disorder and disorder increases with with less rigidity of a substance. If the reactants are mainly liquids and solids and the products are all gases, then you know the entropy is increasing.

Grace Han 2K
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Joined: Tue Nov 15, 2016 3:00 am

### Re: entropy sign

gas>> liquid >> solid

If a rxn has only gas molecules, then you can subtract the number of moles from the product to the reactant. If it is negative, then the change in entropy is negative. If it is positive, then the change in entropy is positive for the forward reaction.

example
2CO(g) + O2(g) --> 2CO2(g)

2mol- (2mol- 1mol)= -1mol

This rxn has a negative change in entropy.

Ishita Monga 1B
Posts: 31
Joined: Thu Jul 27, 2017 3:00 am

### Re: entropy sign

If the mols of gas are increasing as a result of the reaction, entropy is +. If the mols of gas are decreasing, entropy is -.
If the reactants are changing from solid to liquid or liquid to gas, entropy is +. If they are changing from gas to liquid or liquid to solid, entropy is -.

Veritas Kim 2L
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Joined: Fri Sep 29, 2017 7:05 am

### Re: entropy sign

Do we have to indicate the signs of entropy?

AtreyiMitra2L
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### Re: entropy sign

If there is net increase of gaseous moles --> increase in entropy. If there is a net decrease --> decrease in entropy. If appearence of aqueous, net increase. if we see an increase in molecular complexity with the products --> net increase.