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annikaying wrote:What is most important in deciding if a reaction is spontaneous (ex enthalpy, entropy, Gibbs free energy)?
Personally, I think that Gibbs free energy is the best indicator because it combines enthalpy and entropy. Moreover, it's extremely clear cut: if delta G is negative, it is spontaneous; if delta G is positive, it is not spontaneous. However, this does not mean that you can't estimate if a reaction is spontaneous or not using enthalpy or entropy. It's just that Gibbs free energy is much more clear cut.
As everyone above said, Gibbs free energy is how you determine if a reaction is spontaneous or not. However, it might be important to remember that the reason Gibbs free energy is so clear cut is that it’s because it’s based off total entropy which is always increasing.
Delta G is the greatest determiner of whether a reaction will be spontaneous or not. If delta G is negative, then the reaction is spontaneous. You could also use the equation DeltaG= DeltaH- T*DeltaS, given either DeltaH or DeltaS, to see what values need to be in order to produce a spontaneous reaction.
If a reaction has an increase in entropy or a decrease in enthalpy, then it is more likely to be spontaneous. To compute the actual value you need to check if the Gibbs free energy of a reaction is negative and to do that you use the equation delta G=deltaH-T*deltaS
Natalie Benitez 1E wrote:Why exactly does delta G have to be negative to be considered spontaneous?
If delta G is negative that means it is going from higher energy(reactants) to lower energy (products). If it is going from high to low, you need very little (if any input of energy) so it will happen spontaneously.
On the other hand when Delta G is positive, it is going from lower energy of reactants to higher energy of products. Because it is going from low to high, it needs an input of energy. The reaction will not take place unless there is this input which. is why it is not spontaneous
To add on, when Gibbs free energy is negative that means that according the equation for gibbs free energy, delta S or change in entropy is positive and if change in entropy is positive, it means that a process is spontaneous.
Gibbs free energy is the best and most accurate way to tell whether a reaction is spontaneous, but using the equation delta G= delta H- T*delta S, it is possible to see what values of delta H and delta S gives a a negative delta G value.
Gibbs free energy is defined by a combination of enthalpy, temperature, and entropy. If Gibbs free energy is negative, that means the reaction is spontaneous, and if it is positive, the reaction will not be spontaneous. Note, spontaneity does NOT mean that the reaction will just proceed quickly, just that it is thermodynamically favorable. The largest factor is definitely enthalpy. Entropy can play a small role, but enthalpy usually dominates the spontaneity of a reaction.
DeltaG = DeltaH - DeltaS * T, when Delta G is negative, it is spontaneous, it can be negative when delta H is negative and Delta S is positive or high negative delta H and small negative deltaS or small positive deltaH and high positive DeltaS
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