Q1: a) Write a balanced chemical equation that shows the precipitation reaction

Question

Q1: a) Write a balanced chemical equation that shows the precipitation reaction that could occur between Cu2+ (aq) and S2 (aq).

b) If the concentration of Cu2+ is 0.50 M and the concentration of S2 is 0.40 M and both solutions will be diluted by a factor of 2, write an expression for the reaction quotient, Q, for the above reaction.

c) Use Equations (6) and (7) along with the calculated value of Q from part (b) to determine both !Grxn o and! !Grxn for this reaction. Use the table in your textbook to look up the standard free energies of formation for Cu2+ (aq), S2 (aq), and CuS(s).

Explanation / Answer

1 a) Cu+2 + S2- = CuS

b)

initial concentraion of Cu+2 = 0.50 M

since its diluted by a factor of 2, new concentration =0.25 M

initial concentraion of S- = 0.50 M

since its diluted by a factor of 2, new concentration =0.25 M

reaction quotient = [CuS]/[Cu+2][S2- ] = 1/0.252 = 16

c.

free energy of formation of Cu+2 = 65.49 kj/mol

free energy of formation of S2-= 85.8 kj/mol

free energy of formation of CuS = -53.6 kj/mol

G0 of the reaction =[ -53.6 - (85.8+65.49)] kj/mol= -204.89 kj/mol

G = G0 + RT ln Q

= -204.89 + 8.314*298 ln (16)

= -6.664 Mj/mol

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