## deltaS/R

$\ln K = -\frac{\Delta H^{\circ}}{RT} + \frac{\Delta S^{\circ}}{R}$

ursulavictorino1K
Posts: 55
Joined: Sun Feb 17, 2019 12:15 am

### deltaS/R

Why do we ignore the deltaS/R when we are comparing T1 and T2?

Hope Hyland 2D
Posts: 50
Joined: Wed Feb 20, 2019 12:16 am

### Re: deltaS/R

I'm not sure what you mean, could you give an example of what you're referring to?

Ashley Wang 4G
Posts: 103
Joined: Wed Sep 11, 2019 12:16 am

### Re: deltaS/R

We don't ignore ∆S/R when deriving the equation. Maybe the term appears to "disappear," but it's actually just cancelled out when we subtract one lnK1 equation from the other (lnK2).

If you're referring to why we can assume ∆S and ∆H are independent of temperature, it is just an assumption we make that isn't exactly true in reality, but allows for simpler estimations.

Hope this cleared things up!

Sydney Pell 2E
Posts: 100
Joined: Wed Sep 11, 2019 12:17 am

### Re: deltaS/R

When comparing temperatures, deltaS and deltaH are assumed to stay constant for both temperatures which could be why deltaS/R seems to be ignored.

505316964
Posts: 95
Joined: Thu Jul 11, 2019 12:17 am

### Re: deltaS/R

In the equation you use to compare two temperatures you don't ignore deltaS/R it's just canceled out when subtracting the equations lnK(2)-lnk(1), lnk= (-delta H naught/RT) - (delta S naught/R).

Labiba Sardar 2A
Posts: 103
Joined: Sat Jul 20, 2019 12:15 am

### Re: deltaS/R

Sydney Pell 2E wrote:When comparing temperatures, deltaS and deltaH are assumed to stay constant for both temperatures which could be why deltaS/R seems to be ignored.

Why can you assume that delta S is constant when you're using the van't Hoff equation to compare temperatures?

Brian_Ho_2B
Posts: 221
Joined: Fri Aug 09, 2019 12:16 am

### Re: deltaS/R

Labiba Sardar 2A wrote:
Sydney Pell 2E wrote:When comparing temperatures, deltaS and deltaH are assumed to stay constant for both temperatures which could be why deltaS/R seems to be ignored.

Why can you assume that delta S is constant when you're using the van't Hoff equation to compare temperatures?

We can assume that the delta S (not) is constant because it is the delta S for that specific reaction at standard conditions, so there's only one value for delta S (not). At different temperatures, the delta S (not) at standard conditions is still constant, because it's the value at standard conditions.

805097738
Posts: 180
Joined: Wed Sep 18, 2019 12:20 am

### Re: deltaS/R

they aren't ignored, the just get cancelled out when deriving the new equation