Entropy V.S Enthalpy QUestion

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Entropy V.S Enthalpy QUestion

Postby 504999222 » Thu Feb 06, 2020 11:39 am

I'm not sure if this always applies, but if enthalpy is negative and the entropy is negative, would that mean both are spontaneous?
If so then would that same question apply if both enthalpy and entropy were positive? Or if one is positive and the other is negative?

Aman Sankineni 2L
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Re: Entropy V.S Enthalpy QUestion

Postby Aman Sankineni 2L » Thu Feb 06, 2020 1:08 pm

I think the table on this page does a good job of answering your question, though it also depends on temperature:

https://opentextbc.ca/introductorychemi ... erature-2/

Ryan Lee 1E
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Re: Entropy V.S Enthalpy QUestion

Postby Ryan Lee 1E » Thu Feb 06, 2020 1:21 pm

Spontaneity would be determined by free energy, whose equation is deltaG = deltaH - TdeltaS. It's not just if enthalpy (H) or entropy (S) is a certain value, but the both in combination would have to work together to make something spontaneous. On that note, a positive deltaS indicates that entropy is increasing, which means it would contribute to deltaG being spontaneous (not what you said about entropy being negative). Typically for something to be spontaneous, deltaH would have to be negative exothermic and deltaS would have to be positive increasing entropy. In context, this also makes sense since since entropy increasing means the system is approaching equilibrium, which is something a system wants to do.

Louise Lin 2B
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Re: Entropy V.S Enthalpy QUestion

Postby Louise Lin 2B » Sun Feb 09, 2020 11:23 pm

Not necessarily, spontaneous and nonspontaneous would have to depend on how large the values of entropy and enthalpy are compared to each other. For example, if both entropy and enthalpy were negative, it is still possible for the overall reaction to be nonspontaneous if the value of entropy multiplied with temperature (-TdeltaS) is larger than a negative enthalpy.

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