Ethene (C2H4) can be halogenated by the following reaction: C2H4(g)+X2(g)C2H4X2(

ID: 927979 • Letter: E

Question

Ethene (C2H4) can be halogenated by the following reaction: C2H4(g)+X2(g)C2H4X2(g) where X2 can be Cl2, Br2, or I2.

1. Use the thermodynamic data given to calculate H for the halogenation reaction by I2 at 17 C.

2. Use the thermodynamic data given to calculate S for the halogenation reaction by I2 at 17 C.

3. Use the thermodynamic data given to calculate G for the halogenation reaction by I2 at 17 C.

4. Use the thermodynamic data given to calculate Kp for the halogenation reaction by I2 at 17 C.

When collecting data, pay attention to the physical state : (g)

dH, kJ/mol dS, J/mol.K

C2H4Cl2(g)   dH= -129.7   dS = 308.0
C2H4Br2(g)   dH= -38.3    dS= 330.6
C2H4I2(g)      dH= 66.5      dS= 347.8

Cl2 (g) 0 223

Br2 (g) 31 245

I2 (g) 62 261

C2H4(g) 52 219

C2H4(g)+X2(g)C2H4X2(g)

dH may be considered as not depending on temperature.

dH = dHC2H4X2 – dHC2H4 – dHX2 = dHC2H4X2 - 52 – dHX2

E.g. for C2H4Cl2(g) dH = -129.7 -52 -0 = - 181.7 kJ/mol

But for C2H4Br2(g) dH = -38.3 -52 - 31= - 121.3 kJ/mol

for C2H4I2(g dH = 66.5 – 52 – 62 = - 47.5 kJ/mol

dS is not temperature dependent

dS = dSC2H4X2 – dSC2H4 – dSX2

E.g. for C2H4I2(g) dS = 347.8 – 219 - 261 = -132.2 J/mol.K

dG is temperature dependent

dG=dHo-TdSo

Pay attention to measurement units dH, kJ/mol but dS, J/mol.K

E.g. for C2H4I2(g) dG = - 47.5 kJ/mol – 290K x (-0. 1322 kJ.mol.K) = - 9.2 kJ/mol

Pay attention to measurement units

lnKp = - dG/RT , it depends on temperature

= 9200 J/(8.314 J/mol.K x 290 K)=

= 3.816

Kp = e3.816 = 45.4

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