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#### ziccoh

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##### check some HW, thanks
« 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

what am i doing wrong?

thanks i lot for your help

ziccoh

#### Borek

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##### Re: check some HW, thanks
« Reply #1 on: August 07, 2008, 03:04:34 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.
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