How to tell what happens to entropy by seeing a reaction?

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Fenared Ortiz 3K
Posts: 37
Joined: Wed Nov 16, 2016 3:03 am

How to tell what happens to entropy by seeing a reaction?

Postby Fenared Ortiz 3K » Fri Feb 02, 2018 1:50 pm

C12H22O11(s) + O2(g) ---> CO2(g) +H2O(l)

Given this equation how would we be able to tell what happens to entropy?

Andy Nguyen 1A
Posts: 56
Joined: Thu Jul 27, 2017 3:00 am

Re: How to tell what happens to entropy by seeing a reaction?

Postby Andy Nguyen 1A » Fri Feb 02, 2018 1:56 pm

Normally, combustion reactions result in an increase in entropy. Based on the phase changes, we see that a solid changed into a gas and liquid, which means an increase in entropy.

Sue Xu 2K
Posts: 58
Joined: Fri Sep 29, 2017 7:06 am

Re: How to tell what happens to entropy by seeing a reaction?

Postby Sue Xu 2K » Fri Feb 02, 2018 7:56 pm

You can just generally look at the phase of the phase of the reactants and products. In this reaction, the reactants are 1 solid and 1 gas, while the products are 1 liquid and 1 gas. Because liquid has higher entropy than solid, the entropy of the products is higher.

Cynthia Tsang
Posts: 52
Joined: Fri Sep 29, 2017 7:07 am
Been upvoted: 1 time

Re: How to tell what happens to entropy by seeing a reaction?

Postby Cynthia Tsang » Sat Feb 03, 2018 11:44 am

Like mentioned above, since the entropy of the products is higher, the total entropy would be a positive value.

David Minasyan 1C
Posts: 54
Joined: Thu Jul 13, 2017 3:00 am

Re: How to tell what happens to entropy by seeing a reaction?

Postby David Minasyan 1C » Sat Feb 03, 2018 11:56 am

Generally speaking, the entropy for gas > liquid > solid.

Phillip Winters 2F
Posts: 50
Joined: Fri Sep 29, 2017 7:05 am

Re: How to tell what happens to entropy by seeing a reaction?

Postby Phillip Winters 2F » Sat Feb 03, 2018 5:54 pm

The phase of the reactants and products are the best way of looking at a reaction and determining how entropy changes, and entropy increases from solid to liquid to gas

Garret G 2F
Posts: 24
Joined: Fri Sep 29, 2017 7:06 am

Re: How to tell what happens to entropy by seeing a reaction?

Postby Garret G 2F » Sat Feb 03, 2018 6:41 pm

This youtube does a really good job of explaining how to predict changes in entropy: https://www.youtube.com/watch?v=ro3AnXdajAM


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