Why Does OH- Have a Negative Standard Molar Entropy?

  • Thread starter Thread starter Trowa
  • Start date Start date
  • Tags Tags
    Entropy Negative
AI Thread Summary
The discussion centers on the negative standard molar entropy of the hydroxide ion (OH-), contrasting it with the positive values of H+ and H2O. Participants reference the textbook "Physical Chemistry" by Atkins, which suggests that the negative entropy arises from the increased order when OH- is added to water. This phenomenon may be due to the strong repulsion between anions in solution, leading to a lower entropy compared to a hypothetical isolated state. The conversation highlights the complexities of measuring entropy in different states and solutions. Understanding these concepts is crucial for grasping the behavior of ions in aqueous environments.
Trowa
Messages
6
Reaction score
0
Hi there!

The Standard molar entropy of H+ and H2O are positive.
But OH- has a negative standard molar entropy.
Can somebody explain why the standard molar entropy of OH- is negative?

I just can't imagine how entropy could be negative.

Thanx in advance!
 
Physics news on Phys.org
What reference are you looking at?
 
Mapes said:
What reference are you looking at?

Physical chemistry (Atkins) - 8th edition
And this question appeared on my exam.

Do you know more about negative entropy?
 
It looks like Atkins is talking about the partial molar entropy of the molecule in solution; the addition of the molecule to water increases order.
 
That makes sense; pure OH- could than still be positive but that is hard to isolate. Maybe the entropy is lower in water because the anions can be closer together than without solution (strong repulsion) (basically: the reference point must be higher in entropy).

Thanx!
 

Thread 'Struggling to understand the concept of this question (ice cube in water optics question)'

TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
View full post »
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

How to Calculate the Molar Entropy of H2O(g) at 25°C and 1 bar?
Replies
9
Views
2K
Chemical thermodynamics, entropy, Maxwell relation and Z
Replies
1
Views
1K
How does reversible =>no entropy change in the universe?
Replies
20
Views
3K
Entropy change mixing oil and water question
Replies
7
Views
5K
I Entangled, mixed state with conditional entropy zero
Replies
1
Views
1K
Thermodynamics: Possible process between a van der Waals gas and an ideal gas
Replies
1
Views
2K
Entropy change for water in contact with a reservoir
Replies
4
Views
4K
Does work have the same impact on entropy change as heat?
Replies
2
Views
1K
Entropy and the Laws of Thermodynamics
Replies
3
Views
1K
Entropy change and reversible/irreversible processes
Replies
1
Views
2K

Hot Threads

Recent Insights

Back
Top