## Spontaneous reactions

Hanniel U 2B
Posts: 76
Joined: Fri Sep 28, 2018 12:16 am

### Spontaneous reactions

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

505211599
Posts: 60
Joined: Fri Sep 28, 2018 12:28 am

### Re: Spontaneous reactions

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
Posts: 60
Joined: Fri Sep 28, 2018 12:23 am

### Re: Spontaneous reactions

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
Posts: 59
Joined: Fri Sep 28, 2018 12:20 am

### Re: Spontaneous reactions

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
Posts: 68
Joined: Fri Sep 28, 2018 12:26 am

### Re: Spontaneous reactions

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
Posts: 61
Joined: Fri Sep 29, 2017 7:03 am

### Re: Spontaneous reactions

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
Posts: 75
Joined: Fri Sep 28, 2018 12:26 am

### Re: Spontaneous reactions

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
Posts: 39
Joined: Fri Sep 28, 2018 12:17 am

### Re: Spontaneous reactions

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
Posts: 50
Joined: Tue Feb 26, 2019 12:16 am

### Re: Spontaneous reactions

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

Jacob Villar 2C
Posts: 105
Joined: Sat Aug 17, 2019 12:18 am

### Re: Spontaneous reactions

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