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

Answer – We are given, , Ksp at different temperature and need to calculate the Gosoln at each temp.

We know the formula ,

Go = -RTln K

1)Gosoln at 15oC , K = 2.89*10-2

T = 15 +273 K = 288 K

Gosoln = - 8.314 J.mol-1.K-1 * 288 K * ln 2.89*10-2

Gosoln= 8485.7 J

            = 8.486 kJ/mol

2) Gosoln at 31oC , K = 4.11*10-2

T = 31 +273 K = 304 K

Gosoln = - 8.314 J.mol-1.K-1 * 304 K * ln 4.11*10-2

Gosoln= 8067 J

            = 8.067 kJ/mol

3) Gosoln at 51oC , K = 6.08*10-2

T = 51 +273 K = 324 K

Gosoln = - 8.314 J.mol-1.K-1 * 324 K * ln 6.08*10-2

Gosoln= 7542.9 J

            = 7.543 kJ/mol

4) Gosoln at 70oC , K = 8.45*10-2

T = 70 +273 K = 343 K

Gosoln = - 8.314 J.mol-1.K-1 * 343 K * ln 8.45*10-2

Gosoln = 7046.6 J

            = 7.047 kJ/mol

From the observing the given data as the temperature increase solubility product of the salt increase, means solubility of salt also increase and salt gets soluble.

We know the standard free energy is positive, means process is non-spontaneous in forward direction, so the change in enthalpy is positive when salt dissolve there is heat absorbed, so this is endothermic process.

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