entropy sign


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itzeelpadillaDis1A
Posts: 52
Joined: Fri Sep 29, 2017 7:03 am

entropy sign

Postby itzeelpadillaDis1A » Sun Feb 11, 2018 7:48 pm

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

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

Re: entropy sign

Postby Julianna Thrasher 1B » Sun Feb 11, 2018 8:29 pm

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
Posts: 33
Joined: Tue Nov 15, 2016 3:00 am

Re: entropy sign

Postby Grace Han 2K » Mon Feb 12, 2018 3:00 pm

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

Postby Ishita Monga 1B » Mon Feb 12, 2018 3:25 pm

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
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

Re: entropy sign

Postby Veritas Kim 2L » Mon Feb 12, 2018 8:36 pm

Do we have to indicate the signs of entropy?

AtreyiMitra2L
Posts: 169
Joined: Fri Sep 29, 2017 7:03 am
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Re: entropy sign

Postby AtreyiMitra2L » Mon Feb 12, 2018 8:38 pm

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.


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