Spontaneous reactions

[Hanniel U 2B]

Are exothermic reactions usually spontaneous because energy is released from the system or is there another way to explain it?

[505211599]

an exothermic reaction is usually spontaneous but if there is a large enough decrease in entropy, the gibb's free energy can be positive, thus making the reaction non-spontaneous.

[arif_latif_2G]

Not necessarily. If the Gibbs Free Energy is negative, then the reaction is spontaneous, which can be attributed to a reaction that is very exothermic; however, just being an exothermic reaction does not mean the reaction is spontaneous.

[Angel Chen 2k]

It is Gibbs free energy that determines spontaneity, not the enthalpy of the reaction. The reaction would only be spontaneous if Gibbs free energy is negative.
ΔG=ΔH−TΔS
This equation could be positive even if the enthalpy is negative ( exothermic) with a high enough temperature.

[804994652]

You just want to make sure delta G is negative. So if the equation (ΔG=ΔH−TΔS) is manipulated in a way in which delta G is negative, it is spontaneous.

[Alexa_Henrie_1I]

Many homework problems ask to solve for the temperature at which a reaction is spontaneous. This shows that spontaneity depends on more than it just being exothermic or endothermic and understanding this makes solving these problems easier.

[Karan Thaker 2L]

Not always, you could have a negative entropy. This would give you negative - positive, and if the entropy is large enough it could become larger than the negative value and make delta G positive. Always refer back to the equation G = H - TS

[Roberto Gonzalez 1L]

Gibbs free energy determines spontaneity, not enthalpy alone. However it does play a role. Using the equation ΔG= ΔH- TΔS and making a chart for positive and negative values of ΔS and ΔH should help you better determine what conditions are necessary for spontaneity of the forward reaction.

[Julia Holsinger_1A]

Does gibbs free energy determine spontaneity and enthalpy? Or only enthalpy?

[Jacob Villar 2C]

Not necessarily, as the equation for Gibbs free energy depends on the values for enthalpy, entropy, and temperature.

[Leily Garcia 1C]

A low activation energy can result in the reaction being spontaneous. Not all exothermic reactions are not necessarily spontaneous.

ΔG=ΔH−TΔS
For exothermic reactions, ΔH is negative. For a spontaneous process, ΔG should be negative. Thus, decrease in enthalpy (−ΔH) contributes significantly to make ΔG negative.

[405718358]

Usually the exothermic reaction is spontaneous a way to determine if it is all you can do is just check to see if delta G is negative. If delta G is positive them we can determine and say that it is non-spontaneous