Spontaneous reactions

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

Spontaneous reactions

Postby Hanniel U 2B » Sun Feb 17, 2019 6:42 pm

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

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

Re: Spontaneous reactions

Postby 505211599 » Sun Feb 17, 2019 6:52 pm

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
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Joined: Fri Sep 28, 2018 12:23 am

Re: Spontaneous reactions

Postby arif_latif_2G » Sun Feb 17, 2019 6:55 pm

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
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Re: Spontaneous reactions

Postby Angel Chen 2k » Wed Feb 20, 2019 12:27 am

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
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Joined: Fri Sep 28, 2018 12:26 am

Re: Spontaneous reactions

Postby 804994652 » Sun Feb 24, 2019 11:34 pm

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
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Joined: Fri Sep 29, 2017 7:03 am

Re: Spontaneous reactions

Postby Alexa_Henrie_1I » Sat Mar 02, 2019 6:50 pm

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
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Re: Spontaneous reactions

Postby Karan Thaker 2L » Sat Mar 02, 2019 7:40 pm

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
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Re: Spontaneous reactions

Postby Roberto Gonzalez 1L » Sun Mar 17, 2019 6:06 pm

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
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Joined: Tue Feb 26, 2019 12:16 am

Re: Spontaneous reactions

Postby Julia Holsinger_1A » Sun Jan 26, 2020 10:48 pm

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

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

Re: Spontaneous reactions

Postby Jacob Villar 2C » Sun Jan 26, 2020 10:51 pm

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


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