You dissolve 8.000 g of KC1_(s)) in an insulated container of 92.000 g of water

Question

You dissolve 8.000 g of KC1_(s)) in an insulated container of 92.000 g of water (resulting in a solution with a total mass of 100.000 g). This results in a change in temperature of the solution of-4.2 degree Celsius. Assuming that the specific heat capacity of this solution is 4.184J/(g degree Celsius) and based upon the energy of formation values transcribed from your lab manual, please calculate the entropy (Delta S) for this reaction at 298 K. KC1_(S) Delta Gf degree = -408.3 kJ/mol K^+_(aq) Delta Gf degree = -283.2 kJ/mol Cl-_(aq) Delta Gg degree = -131.2 kJ/mol

Explanation / Answer

KCl(aq) -----> K+(aq) + Cl-(aq)

delta G0rkn = delta G0f Cl- + delta G0f H+ - delta G0f KCl = -6.1 kJ/mole

Now, moles of KCl in 8 g of it = mass/molar mass = 8/74.5 = 0.107

thus, delta Grkn = -6.1*0.107 = -0.655 kJ/mole

Now, delta Hrkn = mass of solution*specific heat of the solution*change in temperature = -100*4.184*4.2 = -1757.28 J = -1.757 kJ

Now, delta G = delta H - T*delta S

Thus, delta S = (-1.757 + 0.655)/298 = -0.0037 kJ/K = -3.7 J/K

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