111davey1
Badges: 14
Rep:
?
#1
Report Thread starter 2 years ago
#1
Hi,
Say you had an endothermic reaction with a positive entropy change. I can understand that the products would have more heat content and therefore more energy than the reactants but my understanding is that the positive entropy change would mean that this energy is more dispersed and not available to do anything. But, my book says that for a reaction to be feasible there must be a decrease in the overall energy derived from both the enthalpy change and entropy of the system.

My question is that i can understand how a decrease or increase in enthalpy will change the heat content of the products and therefore the energy of the system but not how entropy can change the energy of the system as from my understanding this just means the energy becomes more dispersed??

Thanks for any help
0
reply
EierVonSatan
Badges: 21
#2
Report 2 years ago
#2
Are you asking what entropy is? It's not the same as energy. Have you seen the following equation?

ΔG = ΔH - TΔS

Entropy change is the difference in number of different states a given system can be in. More disorder = more ways the system can be arranged in these different states. The second law of thermodynamics states that the entropy of an isolated system never decreases so for a process to be feasible ΔG < 0. Either the surroundings gain thermal energy (negative enthalpy change, which increases the disorder to the surroundings) or the system gains entropy internally (or both obviously).
1
reply
111davey1
Badges: 14
Rep:
?
#3
Report Thread starter 2 years ago
#3
(Original post by EierVonSatan)
Are you asking what entropy is? It's not the same as energy. Have you seen the following equation?

ΔG = ΔH - TΔS

Entropy change is the difference in number of different states a given system can be in. More disorder = more ways the system can be arranged in these different states. The second law of thermodynamics states that the entropy of an isolated system never decreases so for a process to be feasible ΔG < 0. Either the surroundings gain thermal energy (negative enthalpy change, which increases the disorder to the surroundings) or the system gains entropy internally (or both obviously).
Thanks, my book says for G to be negative there must be an overall decrease in energy (which would make the reaction feasible). That would suggest the energy derived from entropy is T*S. Is this true?
0
reply
EierVonSatan
Badges: 21
#4
Report 2 years ago
#4
(Original post by 111davey1)
Thanks, my book says for G to be negative there must be an overall decrease in energy (which would make the reaction feasible). That would suggest the energy derived from entropy is T*S. Is this true?
Well, the units for the TΔS term is K * J/K = J so it is an energy term
1
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • University of Bristol
    Undergraduate Open Afternoon Undergraduate
    Wed, 23 Oct '19
  • University of Exeter
    Undergraduate Open Day - Penryn Campus Undergraduate
    Wed, 23 Oct '19
  • University of Nottingham
    Mini Open Day Undergraduate
    Wed, 23 Oct '19

Have you made up your mind on your five uni choices?

Yes I know where I'm applying (154)
59.46%
No I haven't decided yet (60)
23.17%
Yes but I might change my mind (45)
17.37%

Watched Threads

View All