[plasticfood]

the solubility of AgCl in water is 3.97 * 10^-6 M @ 0 Celsius and 1.91 * 10^-4 M @ 100 Celsius. Calculate the Ksp for AgCl for both temperatures.

So is ksp = [Ag+][Cl-]? the first ksp = (3.97 * 10^-6)(3.97 * 10^-6)?

[UG]

So is ksp = [Ag+][Cl-]? the first ksp = (3.97 * 10^-6)(3.97 * 10^-6)?

Yes exactly

[plasticfood]

and one last question, i need to calculate delta S from the same problem above. it says delta S is equal to b in the equation y = mx + b. i know how to solve for the slope, but how do i find the y-intercept?

[UG]

and one last question, i need to calculate delta S from the same problem above. it says delta S is equal to b in the equation y = mx + b. i know how to solve for the slope, but how do i find the y-intercept?

Read off the graph?
If there isn't one, you'll probably need to give us a bit more information on the question.

[plasticfood]

i'm not given a graph, but i think i'm still using the same info as the first question: the solubility of AgCl in water is 3.97 * 10^-6 M @ 0 Celsius and 1.91 * 10^-4 M @ 100 Celsius.

so do i graph ln ksp vs. 1/T?? there's another question that ask to solve for delta H, so i use the slope formula and solve for m, so then i can use m = -delta H / 8.314. but how do i find the y-intercept to solve for delta S?  

[UG]

Hi plasticfood, please be specific in what the question asked. At the moment I am slightly lost (although it sounds like you calculated the Gibbs free energy at each temperature )

[plasticfood]

ok so this is the worksheet: http://imgur.com/0HyaX

i am stuck on #3, but now i'm not quite sure if i did #2 right either.
i am just confused b/c the way i figure out delta H and S from the lab is looking at the equation of the line, but now i don't have the equation i guess??  

[UG]

Ok, I see now
So what you need to do is firstly calculate the Gibbs free energy change of the reaction at each temperature.
The formula is ΔG = -RT ln K_sp so you should get two values for ΔG, one at 0^oC and one at 100^oC (but remember in the formula T is in Kelvin). Then the formula you use to plot your line is ΔG = ΔH - TΔS
So you need to plot ΔG vs. T (in Kelvin). The slope of this graph will be -ΔS and the y-intercept will be ΔH.

[plasticfood]

the first delta G is -3.56e-8 and the second is -1.1317e-4. i've tried plotting this in excel, but the graph is not coming out right. i know to how to manually solve for the slope of the line, but how do i manually solve for the y-intercept?   

[UG]

the first delta G is -3.56e-8 and the second is -1.1317e-4. i've tried plotting this in excel, but the graph is not coming out right. i know to how to manually solve for the slope of the line, but how do i manually solve for the y-intercept?    

I don't know how you got negative values 
For the first temperature 0^oC, then ΔG = -RT ln K_sp The K_sp you have worked out to be (3.97 * 10^-6)²
You should then get ΔG = -8.314 * 273.15 * ln (3.97 * 10^-6)² = 56486.9 J

[UG]

I got this...

[plasticfood]

opps i forgot the ln...

ok so delta S is -33.543 and delta H is 65649 J? i'm still a bit confused about this b/c in the lab, it says to plot ln ksp vs 1/T, and find these values using the equation of the line. is what you graph basically the same thing? if i were to graph ln ksp vs. 1/T, then my slope would be 775.4, and delta H would be -6446.47 which is not the same.     

[UG]

Ok I can only assume that if you were to plot ln K_sp vs. 1/T the equation  ΔG = -RT ln K_sp has been rearranged to give ln K_sp = -ΔG/RT. Plotting ln K_sp vs. 1/T would then give you a line with slope -ΔG/R. You would then multiply the slope by R to get G, and then find ΔH and ΔS using the formula ΔG = ΔH - TΔS. I don't know how much of this stuff you have been taught and my assumption could be totally wrong and you are actually meant to be doing something totally different   

[plasticfood]

yeah i think the formula's rearranged. but it says that the slope is -delta H/R.

i finally got excel to work and plotted ln ksp vs 1/T, and got y = 775.4x - 24.88. from here, i can solve for delta S and H, i think.  

[UG]

Great, see if they match what I got