Page 1 of 1

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

Posted: 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?

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

Posted: 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.

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

Posted: 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.

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

Posted: 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.

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

Posted: Sat Feb 03, 2018 11:56 am
Generally speaking, the entropy for gas > liquid > solid.

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

Posted: 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

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

Posted: 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