Question

Ni2+(aq) + 6 NH3(aq) ⇌ Ni(NH3)6 2+(aq)

is Kf = 5.6 × 108 at 25°C.

(a) What is ΔG o
at this temperature?

(b) If standard-state concentrations of reactants and products are mixed, in which
direction does the reaction proceed?

(c) Determine ΔG when [Ni(NH3)62+] = 0.010 M, [Ni2+] = 0.0010 M, and [NH3] = 0.0050 M. In which direction will the reaction proceed to achieve equilibrium?

Answer 1

Answer:

a) ΔGº= -49,9 KJ/mol = - 50 KJ/mol

b) The reaction  goes to the right to formation of products

c) ΔG= 84,42 KJ/mol. The direction is to reactive, to the left

Explanation:

a) ΔGº= - RTLnKf

You need to convert Cº to K. 25ºC=298K

Then, ΔGº= - 3,814 J/molK * 298K* Ln(5.6 *10^8)= - 49906 J/mol = -49,9 KJ/mol = - 50 KJ/mol

b) The ΔGº < 0, that means the direct reaction is spontaneous when te reactive and products are in standard state. In other words the reaction goes to the right, to formation of products

c) The general ecuation for chemical reaction is aA + bB → cD + dD. Thus

ΔG=ΔGº + RTLn (([C]^c*[D]^d)/[A]^a*[B]^b)

In this case,

ΔG=ΔGº + RTLn ([Ni(NH3)62+] / [Ni2+]*[NH3]^6 )= 84417 J/mol =84,42 KJ/mol

ΔG >0 means the reaction isn't spontaneous in the direction of the products. Therefore the direction is to reactive, to the left

Answer 2

The change in the free energy under the given conditions is 35 kJ/mol.

What is formation constant?

The formation constant refers to the equilibrium constant for the formation of a complex such as Ni(NH3)6^2+(aq).

To obtain the change in free energy;

ΔGo = -RTlnK

ΔGo = -(8.314 * 298 * ln5.6 × 10^8)

ΔGo = -49.90 kJ/mol

The reaction will proceed forwad since the change in free energy is negative and the reaction is sponteanous.

We now have to obtain Q from the data given;

Q = 0.010 M/(0.0010 M) (0.0050 M)^6

Q = 6.4 * 10^14

ΔG = ΔGo + RTlnQ

ΔG =  -49.90 * 10^3 + (8.314 * 298 * ln6.4 * 10^14)

ΔG =35 kJ/mol

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