Exo,Endo

[Glycogen]

Advertisement - Members don't see this ad

When a bond is broken,energy is always absorb and we know that.But to explain this,they say:
"since bond forming decreases entropy,it is always exothermic[?].Thus breaking a bond is always endothermic,and requires energy."

Ok,forming a bond will decrease entropy and I am agree with that but we have exothermic reaction when entropy is positive right?
So,I'm a bit confused here!
Would someone explain this?
Thanks

 

[joonkimdds]

When a bond is broken,energy is always absorb and we know that.But to explain this,they say:
"since bond forming decreases entropy,it is always exothermic[?].Thus breaking a bond is always endothermic,and requires energy."

Ok,forming a bond will decrease entropy and I am agree with that but we have exothermic reaction when entropy is positive right?
So,I'm a bit confused here!
Would someone explain this?
Thanks

Endothermic (+delta H) = increase in entropy (+delta S)
Exothermic (-delta H) = decrease in entropy (-delta S)
+ goes with +
- goes with -

 

[klutzy1987]

Endothermic (+delta H) = increase in entropy (+delta S)
Exothermic (-delta H) = decrease in entropy (-delta S)
+ goes with +
- goes with -

Thats not true. There are some bonds which require energy to form and therefore are endothermic reactions and entropy will decrease. There are also bonds which give off energy when formed and increase in entropy. Entropy and Enthalpy are only related by the formula
deltaG=deltaH-TdeltaS

 

[osimsDDS]

When a bond is broken,energy is always absorb and we know that.But to explain this,they say:
"since bond forming decreases entropy,it is always exothermic[?].Thus breaking a bond is always endothermic,and requires energy."

Ok,forming a bond will decrease entropy and I am agree with that but we have exothermic reaction when entropy is positive right?
So,I'm a bit confused here!
Would someone explain this?
Thanks

When were talking about enthalpy, energy is always in the form of heat. So an endothermic reaction where bonds are broken, because it takes energy input to break a bond, and therefore if your breaking a bond your increasing the entropy...
When your forming a bond to make it more stable your giving off heat and therefore heat is lost as energy in order to make the bond. So exothermic would decrease entropy...

Picture the phase diagram in your mind with solid, liquid, gas right...imagine when your breaking bonds going from solid to liquid your going up the chart and therefore the enthalpy will be positive and the entropy would be positive. Now going from gas to liquid, going down making more stable bonds requires the release of energy and therefore enthalpy would be exo and entropy would decrease as well (liquid is less disorder than gas).

This is how it works for me, I had the same problem but some people on here helped me and i dont forget it ever since..

 

[PooyaH]

Endothermic (+delta H) = increase in entropy (+delta S)
Exothermic (-delta H) = decrease in entropy (-delta S)
+ goes with +
- goes with -

That's not right!!!
1. When delta H is - and delta S is + we would have a spontaneous reaction so delta G of system (not universe) is - as well
2. When delta H is + and delta S is - we would have a non-spontaneous reactoin so delta G is + of system is +
3. When delta H is - and delta S is also - we would have a spontaneous reaction only at low temp.
4. When delta H is + and delta S is also + we would have a spontaneous reaction only at high temp.

Whenever delta H is negative its helping towards a spontaneous reaction and whenever delta S is positive its helping towards a spontaneous reaction as well!!!

 

[PooyaH]

When a bond is broken,energy is always absorb and we know that.But to explain this,they say:
"since bond forming decreases entropy,it is always exothermic[?].Thus breaking a bond is always endothermic,and requires energy."

Ok,forming a bond will decrease entropy and I am agree with that but we have exothermic reaction when entropy is positive right?
So,I'm a bit confused here!
Would someone explain this?
Thanks

You can still decrease the entropy of the "system" even if it's an exothermic reaction. but the entropy of the "universe" is always increasing!

 

[joonkimdds]

if we relate delta H and delta S with G, then any kind of combination is possible depends on what's given.
but when we are only talking about delta H and S without G, I believe those two are usually paired, + with +, - with -.(I think)~
For example, making ice = exothermic (-delta H) = decrease in entropy(-delta S).

 

[PooyaH]

if we relate delta H and delta S with G, then any kind of combination is possible depends on what's given.
but when we are only talking about delta H and S without G, I believe those two are usually paired, + with +, - with -.(I think)~
For example, making ice = exothermic (-delta H) = decrease in entropy(-delta S).

Exactly because we have LOW TEMP!!!