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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: ziccoh on August 07, 2008, 02:38:14 PM

Title: check some HW, thanks
Post by: ziccoh on August 07, 2008, 02:38:14 PM

1.
greatest soubility in water of a substance is the one it has the greater Ksp

Ksp 1.3x10^-7 this one is the correct

Ksp 3.5x10^-8


2.
I HAVE A DISSOLUTION OF SODIU  NITRATE  IN WATER THIS OCURS INSTANTANEOUSLY, TEMP WATER DECRESSES, 

AH<0, AS<0, AS<0  IS THE ANSWER I CAME UP WITH
 I indestand spentaneous reactions has to be <0 but im not sure about the rest..

3
and this one I canT FIGURED OUT,
Use the following thermodynamic data

Species---ΔH°(kJ/mol)------S°(J/K mol)
H2O2(l) -187.78---------+109.6
H2O(l) -285.83----------+69.91
O2(g) 0---------------+205.14
to calculate ΔS°univ for the decomposition of hydrogen peroxide at 25.0°C.

2 H2O2(l) → 2 H2O(l) + O2(g)
 

 a.-783.8 J/K
 b.-531.9 J/K
 c.+494.2 J/K
 d.+783.8 J/K
 e.+3741 J/K

what im doing is using

ASuniv=AS sys+AS surrandings 

and to find ASsurran im using

ASsurr=-AHrxn/T So

ASsurr=(2-(-285.83))/298K

=-1.9183 kJ and convert to J/K is -1918.3 J/K

then
ASsystem (2(69.91)+205.14)-(2(109.6))= 125.76

then add ASsysm+Asurra=-1793.3

what am i doing wrong?

thanks i lot for your help

ziccoh

 

 

Title: Re: check some HW, thanks
Post by: Borek on August 07, 2008, 03:04:34 PM

Quote from: ziccoh on August 07, 2008, 02:38:14 PM

greatest soubility in water of a substance is the one it has the greater Ksp

Not necesarilly, AgCl has Kso around 10^-10, so saturated solution is around 10^-5M. Ag₃PO₄ has Kso around 10^-16 - but saturated solution is around 4x10^-5M, so while Kso is smaller, solubility is greater.