What Does \Delta G Indicate in Chemical Reactions?

AI Thread Summary
The Gibbs Free Energy equation is essential for calculating the entropy of the universe, addressing the complexities of entropy changes in surroundings during chemical reactions. When ΔG < 0, the process is spontaneous, indicating that the system releases heat (ΔH < 0) and can also experience an increase in entropy (ΔS > 0). The confusion arises from the misconception that heat release and entropy increase are directly linked; they are not. For example, burning propane increases entropy due to a greater number of gas moles in the products compared to the reactants. Understanding these relationships clarifies the dynamics of chemical reactions and the role of Gibbs Free Energy.
PiRsq
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Homework Statement


A. Explain the need for Gibbs Free Energy equation.
B. Explain what it means when:
\Delta G &lt;0 \Delta G &gt;0 \Delta G =0

Homework Equations



\Delta G= \Delta H-T \Delta S

The Attempt at a Solution



A. Gibbs eqn comes from the need to calculate the entropy of the universe, which is the sum of entropy of system + entropy of surroundings. The need for the Gibbs eqn is because of the problem arising with calculating the entropy of surroundings as there are uncountable entropy changes that take place when heat is released into the surroundings. Gibbs eqn deals with this by eliminating the entropy of surroundings and replacing with an eqn that only has entropy of system on the right side of the eqn.

B. I am confused over here:

If \Delta G&lt;0 then the process is spontaneous. This means\Delta H&lt;0 and \Delta S&gt;0 But how can the system release heat and also have an increase its entropy?
 
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PiRsq said:
I am confused over here:... But how can the system release heat and also have an increase its entropy?

Heat and entropy are not linked. Think of some chemical process for which entropy is clearly increasing. Heat is often given off as well. Burning a hydrocarbon, for example.
 
How about burning of propane. C3H8 + 5O2 ---> 3CO2 + 4H2O + heat

The entropy does increase in this rxn, due to 7 moles of gas in products vs. 6 in the reactants. However, C3H8 is relatively more complex relative to all the other molecules in this rxn. So how can I be sure whether entropy of the system increases, or that of the surroundings
 
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