## Predicting the Sign of Change in S (2010 Final #3)

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

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### Predicting the Sign of Change in S (2010 Final #3)

Quick clarification- how are we able to predict the sign of the change in entropy in a system from an equation? For example, on #3 in the 2010 final, we are given this equation:

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

and we are to conclude that the change in entropy for the system is to be negative.

Niharika Reddy 1D
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### Re: Predicting the Sign of Change in S (2010 Final #3)

We can usually look at the moles of gas to predict the sign of ΔS. If more moles of gas are produced than were initially present as reactants, there is an increase in entropy and ΔS is positive. In this question, since the reactant side has 3 moles of gas whereas the product side has only 2, there's a net decrease in the moles of gas, thus a decrease in entropy as well.

-ΔS means decrease in entropy. The products are more ordered than the reactants.
+ΔS means increase in entropy. The reactants are more ordered than the products.

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