Thermochemistry Quiz (Topic 16)

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• Thermochemistry Quiz (Topic 16)
• Using the data given below valid at 25.0 C and
  1.000 bar
• Fe2O3 (s) 3 C (gr) --gt 2 Fe (s) 3 CO (g) DH
  490.8 kJ
• FeO (s) C (gr) --gt Fe (s) CO (g) DH
  156.1 kJ
• DHf, 298 K CO2 (g) - 393.5 kJ /
  mole
• DHf, 298 K Fe2O3 (s) - 822.3 kJ / mole
• Calculate the enthalpy change in kJ at 25.0 C
  for the reaction
• CO (g) ½ O2 (g) -----gt CO2 (g)

Introduce CO2 (g) using its formation
reaction C (gr) O2 (g) -----gt CO2 (g)
DHf, - 393.5 kJ Introduce CO (g) using the
reverse of the reaction involving hematite, Fe2O3
(s) scaled by 1/3 1/3 3 CO (g) 2 Fe (s)
----gt Fe2O3 (s) 3 C (gr)
DH 1/3 ( - 490.8 kJ ) Note you wouldnt want
to use the reaction involving FeO to introduce
CO, since you have no subsequent way of
eliminating FeO, which does not appear in the net
reaction. Finally, eliminate Fe2O3 (s) using the
reverse formation reaction for Fe2O3 (s)
scaled by 1/3 1/3 Fe2O3 (s) --gt 2 Fe (s) 3/2
O2 (g) DHf - 1/3 (- 822.3 kJ)
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As written, these reactions will add to give the
net reaction CO (g) ½ O2 (g) -----gt CO2
(g) Hence the enthalpies for these reactions will
add to give the heat of the net reaction DH
(- 393.5 kJ / mole) (1/3 (- 490.8 kJ / mole))
(- 1/3 ( - 822.3 kJ / mole ))
- 283.0 kJ