Entropy//Enthalpy ----Exothermic//Endothermic

[pandalove89]

So I understand that if enthalpy is positive than it is endothermic and if enthalpy is negative than it is exothermic.

But how can a positive entropy be exothermic while a negative entropy is endothermic?



For example when you are going from solid to liquid we are absorbing heating so enthalpy would be positive as well as entropy being positive.

In this example: how can an exothermic and endothermic reaction happen at the same time?


Cheers!

---

Members don't see this ad.

 

[JustwantDDS]

s--->l---> g = enthalpy +, entropy + [using energy to break bonds]

g---> l ---> s enthalpy -, entropy - [releasing energy to make bonds]

making bonds- enthalpy - (exothermic, atoms WANT to bond)
breaking bonds- enthalpy + (endothermic, USE energy to break bonds)


i think? correct me if im wrong anyone..

 

[pandalove89]

s--->l---> g = enthalpy +, entropy + [using energy to break bonds]

g---> l ---> s enthalpy -, entropy - [releasing energy to make bonds]

making bonds- enthalpy - (exothermic, atoms WANT to bond)
breaking bonds- enthalpy + (endothermic, USE energy to break bonds)


i think? correct me if im wrong anyone..

yeah, I already know that.

So does this mean that entropy has nothing to do with something being exothermic or endothermic?

 

[rpatel8]

delta G = delta H - T(delta S) . The entropy does not effect whether or not something is exo or endothermic which are terms that refer to enthalpy.

 

[pandalove89]

delta G = delta H - T(delta S) . The entropy does not effect whether or not something is exo or endothermic which are terms that refer to enthalpy.

thank you

 

[rah08e]

thank you

I think I know what you are talking about, Panda. I came across a question that asked "when is a reaction ALWAYS Exothermic?". My original answer was "when Delta G is Negative" but the correct answer was "when Delta H (enthalpy) is Negative"

...I would also like a little overview of the relationship between enthalpy/entropy with exothermic/endothermic. I already know the rules for weather a reaction is spontaneous or non spontaneous.

 

[rpatel8]

I don't understand how you are getting that confused. Delta g has to do with whether or not the reaction is spontaneous. That has nothing to do with the reaction always being endothermic. A reaction with a negative (-) delta H is always exothermic. The words exo and endothermic are only related to delta H (enthalpy). Entropy should not be associated with exo and endo.

 

[rah08e]

I don't understand how you are getting that confused. Delta g has to do with whether or not the reaction is spontaneous. That has nothing to do with the reaction always being endothermic. A reaction with a negative (-) delta H is always exothermic. The words exo and endothermic are only related to delta H (enthalpy). Entropy should not be associated with exo and endo.

Okay thanks. So since -Delta H will always be exothermic, I guess a + Delta H always be endothermic... sounds good to me.

 

[faroo7a]

So I understand that if enthalpy is positive than it is endothermic and if enthalpy is negative than it is exothermic.

But how can a positive entropy be exothermic while a negative entropy is endothermic?



For example when you are going from solid to liquid we are absorbing heating so enthalpy would be positive as well as entropy being positive.

In this example: how can an exothermic and endothermic reaction happen at the same time?


Cheers!

Hey, just remember that entropy"s" is an degree of randomness or disorder. for example when you go from a liquid to gas, you have to add heat to the system that's why it's an (endothermic rxn and therefore enthalpy is +) , but as you do so you are also increasing the disorder or randomness of the substance; therefore entropy increases and it's also positive.

Hope that helps