Question

2 SO2(g) + O2(g) --> 2 SO3(g)

Properties at 25 degrees C

Substance.........delta G standard (kJ/mol)

O2(g).................... 0

SO3(g).................. -371.0

SO2(g).................. -300.1

1. Calculate the Free Energy delta G standard at room temperature (25 degrees C). Determine if the reaction is spontaneous or non spontaneous at 25 degrees C?

2. Calculate K at 25 degrees C for the above reaction.

3. Calculate delta G at 25 degrees C given the following set of partial pressures:

[SO2] = 1M

[O2] = 1M

[SO3] = 100M

Answer 1

2 SO2(g) + O2(g) -----> 2 SO3(g)

d G = 2* 300.1 dG=0 d G = 2* 371

= -600.2 kJ / mole dG = -742 KJ / mole

1) G= product - reactant = - 742 - (-600.2) = `- 141.8 KJ/mole  

the reaction is spontaneous as the G <0 means -ve and is feasible .

2) AS   G = - RT ln K

`- 141.8 = - 8.314 * 298 ln K

ln K =  141.8 / 8.314 * 298 = 141800 / 2477.57 = 57.23

log K= 57.23 / 2.303 = 24.8502

K = anti (24.8502)

K= 7.08 * 10²⁴

3) SO2(g) + O2(g) --> 2 SO3

intial concerntration 2 1 0

equilibrium concerntartion 2-x 1-x 2x

  

K= [SO3]² / [ O2] [SO2] = [100]² / = 10000 (as SO3= 100M )

K= 10⁴ /2 = 5*10 ³

as   

G = - RT ln K = - 8.314 * 298 * 2.303 * log (5 10³)

= - 8.314 * 298 * 2.303 * 3.69   J/mole = - 21054 J/mole = 21.054 KJ/Mole