MSCI 313 Problem set 2 Due Tuesday Feb. 27, 2018 ) is found in some natural envi

Question

MSCI 313 Problem set 2 Due Tuesday Feb. 27, 2018 ) is found in some natural environments. The precipitation reaction for rhodochrosite is Given the following values at 1 atmosphere and 2SC: (a) [Mn2+ 1.00 x 10s M, co,2- 3.5x10. M (b) yMn2-02, yco, 0.21 fr are activity coefficients) (c) Standard free energies of formation (AG) G. kcal/mole Species MnC Mn 54.5 126.0 Calculate: (1) the standard free energy of reaction (AGC) for the precipitation of rhodochrosite (reaction I) (2) the equilibrium constant K for the reaction (3) the free energy of reaction (AG.) at the given seawater conditions (4) the ion activity product (Q) and the reaction quotient p. Note that -Q/K Explain: Based on the results to parts 3 and 4, does the reaction have the potential to occur spontaneously as written?

Explanation / Answer

1) The standard free energy of the reaction is:

Gr = Gproduct – Greactants

= -195 - (-54.5 - 126) = -14.5 kcal/mol

2) The equilibrium constant is

K= aMn * aCO3 = 0.042 where a denotes the activities of the ions.

Thus, K = 0.042

3) The free energy of the reaction at the given seawater condition is:

Gr + RT lnK = G

-14.5 + (1.985 * 10-3) (298) (-3.17)

-14.5 - 1.875 = -16.375 kcal/mol

Thus G = -16.375 kcal/mol

4) Since the reaction is a type of equilibrium reaction,

K = Q

Q = 0.042

Thus, reaction quotient, = 1

Since G is negative, the reaction has the potential to move in the forward direction and it can be regarded as a spontaneous reaction.

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