You measure the solubility of a salt at four different temperatures and calculat

Question

You measure the solubility of a salt at four different temperatures and calculate the following K_sp values: DeltaGdegree_soln for the solubility process is given by the relationship DeltaGdegree_soln =RTlnK_sp where R = 8.314 J/(K*mol) and T is the absolute temperature in degrees K.. Calculate DeltaGdegree_soln (in kj/mol) at each of these temperatures. As the temperature increases, how docs the solubility of the salt change? According to Le ChAtelier's principle, dissolving this salt should therefore be which type of process? In other words, what is the sign of DeltaHdegree_soln?

Explanation / Answer

We can calculate the Delta G of solution for different temperatures by using formula,

Delta G soln= -RTln ksp,

1) 15 dec c= 273=288 k,

Delta G soln= -8.314*288*ln 2.89*10-2,

Delta G soln= -8.314*288*-1.5391,

=-2394.43*-1.5391

=3685.26 KJ,

2) 31 deg c=273+31=304 k,

Delta G SOLN= -RTln ksp,

by putting the values ,

delta G SOLN= -8.3124*304*ln 4.11*10-2,

= -2527.45*-1.3861,

=3503.44 kJ,

3) 51 deg =273+51=324 K,

delta G SOLN= -RT lnksp,

= -8.314*324 ln 6.08*10-2,

= -2693.73* -1.2160,

=3275.83 KJ,

4) 70 DEG C=273+70=343 K,

delta G SOLN= -RT lnksp,

= -8.314*343*ln ksp,

=-2851.70*8.45*10-2,

=-2851.70*-1.073,

=3060.28 KJ,

as the temerature increses solublity of salt increases, according to Le cahtelier's priciple dissolution of salt is endothermic process (from above examples)

the sign of delta G is positive , and also the delta H of soln is possitive,

positive delta H soln is there fore endothermic process.

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