For the reaction I2(s)--->2I(g), delta Ho=+213.6 kJ and delta So=+245.2 J/K. (a)

Question

For the reaction I2(s)--->2I(g), delta Ho=+213.6 kJ and delta So=+245.2 J/K. (a) Calculate delta Go. Is the reaction spontaneous at this temp? Is the reaction spontaneous at this temp? (b) Calculate delta G at 250o C. is the reaction spontaneous at this temp? (c) At what Celcius temp will this reaction be spontaneous? (d) Calculate the thermodynamic equilibrium constant for this reaction at 25oC. Will this be Kp or Kc ? (e) If this reaction occurred in a closed vessel at 25oC until it reached equilibrium, what would the equilibrium pressure of I(g) be? Please show work thank you!

Explanation / Answer

a)

G° = H° - TS° = 213.6 kJ - 298*245.2 J/molK = 213600 - 298*245.2 = 140530.4 J/mol

the reaction isNOT spontanous since G > 0

b)

IF T = 250°C then 523 K

assume:

G° = H° - TS° = 213.6 kJ - 523 *245.2 J/molK = 213600 - 523 *245.2 = 85360.4 J/mol

still G > 0 , therefore not spontanous

c)

at what T is this spontanous?

G = H- TS

assume G<0 then

H - TS < 0

H < TS

T > H/S

T > (213600)/(245.2) = 8900 K

which is pretty high

d)

G° = -RT¨lnK

solve for K

K = exp(140530.4 /(-8.314*298)) = 2.32474*10^-25

This K is actually Kc, since we used R and T (R = 0.082 )

e)

this will never reach equilibrium; since it is strognly favouring reactants

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