Question

Carbon dioxide dissociates to form carbon monoxide.

a. Write down the balanced stoichiometric equation representing the complete dissociation of CO2 to CO

b. determine the equilibrium constant for this reaction at 2000 K

c. Write down the balanced stoichiometric equation when 25% of CO2 has disassociated into CO

d. What is the value of the equilibrium constant when this occurs i.e., when 25% of CO2 has disassociated into CO at 1 bar?

e. At what temperature (approximately) does this occur

f. explain if the complete dissociation of CO2 to CO is an endothermic or exothermic reaction.

g. Finally, determine the enthalpy of this reaction at standard conditions to verify if the complete dissociation of CO2 to CO is endothermic or exothermic

Answer 1

a) The balanced equation for dissociation of CO2 is CO2----->CO +1/2O2

b) for the given reaction, standard enthalpy change = 294 Kj and standard entropy change =

=197.9 +0.5* 205.03- 213.68 =86.735 J/K

assuming enthalpy change does not change, deltaG(2000K)= deltaH- TdeltaS= 294*1000-2000*86.375 =121250 J= 121.25 KJ

from deltaG= -RTlnK, lnK= -121250/(2000*8.314) =-7.29, K= 0.000681

3. 0.25CO2 ---->0.25CO+0.25*0.5O2

4. giver x=0.25, (25% got dissociated )

At equilibrium, CO2=0.75, CO= 0.25 O2=0.125, total moles at equilibrium =0.75+0.25+0.25=1.125

Partial pressures at 1 bar:    Moles fraction* total pressure, mole fraction= moles of the component/total moles

Parital pressures (bar) : CO2=1*(0.75/1.125) =0.67, CO=1*(0.25/1.1250= 0.22, O2= 1-0.67-0.22 =0.11

Kp = (PCO)*(PO2)0.5/ PCO2, where P indicates partial pressure

Kp = 0.22*(0.11)^0.5/0.67=0.108

from ln(K2/K1)= (deltaH/R)*(1/T1-1/T2)

where K= 0.108 at T2 and K1=0.000681 at 2000K

ln(0.108/0.000681)= 5.07 = (294*1000/8.314)*(1/2000-1/T2)

T1= 2804 K

The dissociation of CO2 is endothermic as seen from the gibbs free energy change.